Permanent magnet synchronous motor

ABSTRACT

A synchronous motor includes a stator, a rotor and permanent magnets. The rotor includes a rotor iron core and rotatable relative to the stator, a plurality of conductor bars accommodated within corresponding slots in the rotor iron core. The conductor bars have their opposite ends shortcircuited by respective shortcircuit rings to form a starter cage conductor. The rotor also has a plurality of magnet retaining slots defined therein at a location on an inner side of the conductor bars, in which hole permanent magnets are embedded.

[0001] This application is a divisional application of pending U.S.patent application No. 10/019,286, filed Jan. 2, 2002, which was theNational Stage of International Application No. PCT/JP00/04693, filedJul. 13, 2000, the disclosures of which are expressly incorporatedherein by reference in their entireties. The International was publishedunder PCT Article 21(2) in English.

TECHNICAL FIELD

[0002] The present invention generally relates to a permanent magnetsynchronous motor and, more particularly, to the synchronous motorgenerally used in a motor-driven compressor in a refrigerating system oran air conditioning system or any other industrially utilized electricappliance.

BACKGROUND ART

[0003] A self-starting permanent magnet synchronous motor operates as aninductor motor at the time of starting thereof owing to a startersquirrel cage conductor and as a synchronous motor as rotating magneticpoles created by the permanent magnets are entrained by a rotatingmagnetic field formed by a stator winding and moving angularly at asynchronous speed upon arrival of the rotor at a speed approaching thesynchronous speed. This synchronous motor has an excellent constantspeed operating performance and an excellent high efficiency. Inparticular, various improvement have hitherto been made to a rotorstructure of the synchronous motor.

[0004] For example, the Japanese Patent Publications No. 59-23179 andNo. 63-20105 discloses the prior art rotor structure for theself-starting permanent magnet synchronous motor.

[0005]FIG. 6 illustrates the prior art rotor disclosed in the JapanesePatent Publication No. 59-23179. Referring to FIG. 6, reference numeral1 represents a rotor, and reference numeral 2 represents a rotor ironcore having a plurality of slots 3 defined therein adjacent an outerperiphery thereof. Conductor bars 4 are disposed within those slots 3and have their opposite ends shortcircuited by respective shortcircuitrings to thereby form a starter squirrel cage conductor. Theshortcircuit rings (not shown) are made of an annular electroconductivematerial disposed on axially opposite ends of the rotor iron core andare connected with the conductor bars 4. A plurality of magnet retainingholes 5 are provided on an inner side of the conductor bars 4, withcorresponding permanent magnets 6 embedded therein. Reference numeral 7represents magnetic flux shortcircuit preventive slits that are spacedsuch a small distance P from the magnet retaining holes 5 that magneticsaturation can take place between the magnet retaining holes 5 and theslits 7 to thereby prevent the magnetic fluxes emanating from thepermanent magnets from being shortcircuited between the differentmagnetic poles.

[0006]FIG. 58 illustrates a longitudinal sectional view of the rotorused in the prior art self-starting synchronous motor disclosed in theJapanese Patent Publication No. 63-20105 and FIG. 59 illustrates across-sectional view taken along the line A-A′ in FIG. 58. Referring toFIGS. 58 and 59, reference numeral 11 represents a rotor, and referencenumeral 12 represents a rotor iron core made up of a laminate ofelectromagnetic steel plates. Reference numeral 13 represents conductorbars having their opposite ends connected with respective shortcircuitrings 14 to thereby form a starter squirrel cage conductor. Referencenumeral 15 represents permanent magnets embedded in the rotor iron coreto form four rotor magnetic poles. Reference numeral 16 representsmagnetic flux shortcircuit preventive slits each operable to prevent themagnetic fluxed between the neighboring permanent magnets of thedifferent polarities from being shortcircuited. Reference numeral 17represents an end plate disposed on each of axially opposite ends of therotor iron core 2 by means of bolts to avoid any possible separation ofthe permanent magnets 5 from the rotor iron core 2.

[0007] When the prior art permanent magnet motor of the type providedwith the cage conductor is to be used since the conductor bars and thepermanent magnets are employed as rotatory drive elements, if theconductor bars and the permanent magnets are incorrectly positionedrelative to each other, a force generated from the conductor bars and aforce generated by the permanent magnets will be counteracted with eachother and, therefore, no efficient rotatory drive will be achieved.Also, the permanent magnet motor provided with such a cage conductorrequires a complicated and increased number of manufacturing steps sincethe permanent magnets and the conductor bars are provided in the rotor.

[0008] In view of the foregoing, the present invention is intended tosolve those problems inherent in the prior art permanent magnetsynchronous motor and is to increase the efficiency and simplify themanufacture of the synchronous motor of the type employing the permanentmagnets.

DISCLOSURE OF INVENTION

[0009] To this end, the present invention according to a first aspectthereof provides a synchronous motor which comprises a stator includinga stator iron core having a winding wound therearound, said stator ironcore having an inner cylindrical surface; a rotor including a rotor ironcore and rotatably accommodated while facing the inner cylindricalsurface of the stator iron core, said rotor including a plurality ofconductor bars accommodated within corresponding slots defined in anouter peripheral portion of the rotor iron core, said conductor barshaving their opposite ends shortcircuited by respective shortcircuitrings to form a starter squirrel cage conductor, said rotor having aplurality of magnet retaining slots defined therein at a location on aninner side of the conductor bars; and permanent magnets embedded withinthe magnet retaining holes in the rotor and defining rotor magneticpoles. In this synchronous motor, the neighboring members of the slotsare spaced a distance which is referred to as a slot interval, the slotinterval at a location adjacent one end of rotor magnetic poles beingsmaller than the slot interval at a location adjacent a center point ofthe rotor magnetic poles.

[0010] According to the first aspect of the present invention, themagnetic fluxes emanating from the permanent magnets will hardly leak tothe outer peripheral surface of the rotor at a position adjacentopposite ends of the rotor magnetic poles and, instead leak to the outerperipheral surface of the rotor at a position adjacent a center point ofthe rotor magnetic poles. For this reason, the pattern of distributionof the magnetic fluxes in an air gap between the stator and the rotorrepresents a generally trapezoidal or sinusoidal waveform such that ascompared with the rectangular waveform, the amount of change of themagnetic fluxes per unitary time increases and, therefore, the voltageinduced across the winding of the stator can be increased to therebyintensify the rotor magnetic poles. Accordingly, in the practice of thepresent invention, to secure the required induced voltage, neither isthe volume of the permanent magnets increased, nor the permanent magnetshaving a high residual magnetic flux density are required such asrequired in the prior art, thus making it possible to provide ahigh-performance and inexpensive self-starting synchronous motor havinga required out-of-step torque and a high efficiency.

[0011] If the slot interval at a location spaced from the center pointof the rotor magnetic poles in a direction conforming to a direction ofrotation of the rotor is chosen to be greater than the slot interval ata location spaced from the center point of the rotor magnetic poles in adirection counter to the direction of rotation of the rotor, althoughduring a loaded operation the maximum value of a distribution, on therotor surface, of composite magnetic fluxes of the magnetic fluxes fromthe winding of the stator and the magnetic fluxes from the permanentmagnets is positioned on one side conforming to the direction ofrotation rather than the center point of the rotor magnetic poles, sincethe slot interval of the rotor through which the magnetic fluxes at thatposition pass is increased, the magnetic saturation at that portion canbe prevented. Accordingly, the magnetic fluxes emanating from themagnets can be sufficiently taken from the rotor and, therefore, thecurrent across the stator winding can be suppressed to thereby increasethe efficiency of the motor.

[0012] The present invention according to a second aspect thereofprovides a synchronous motor which comprises a stator including a statoriron core having a winding wound therearound, said stator iron corehaving an inner cylindrical surface; a rotor including a rotor iron coreand rotatably accommodated while facing the inner cylindrical surface ofthe stator iron core, said rotor including a plurality of conductor barsaccommodated within corresponding slots defined in an outer peripheralportion of the rotor iron core, said conductor bars having theiropposite ends shortcircuited by respective shortcircuit rings to form astarter squirrel cage conductor, said rotor having a plurality of magnetretaining slots defined therein at a location on an inner side of theconductor bars; and permanent magnets embedded within the magnetretaining holes in the rotor and defining rotor magnetic poles. In thissynchronous motor, the slots have a radial length that is smaller at acenter point of the rotor magnetic poles, and a distance between one ofthe slots positioned adjacent one end of the rotor magnetic poles andthe magnet retaining holes is smaller than a distance between the slotspositioned at other locations of the rotor and the magnet retainingholes.

[0013] According to the second aspect of the present invention, themagnetic fluxes emanating from the permanent magnets will hardly leak tothe outer peripheral surface of the rotor at a position adjacentopposite ends of the rotor magnetic poles and, instead leak to the outerperipheral surface of the rotor at a position adjacent a center point ofthe rotor magnetic poles. For this reason, the pattern of distributionof the magnetic fluxes in an air gap between the stator and the rotorrepresents a generally trapezoidal or sinusoidal waveform such that ascompared with the rectangular waveform, the amount of change of themagnetic fluxes per unitary time increases and, therefore, the voltageinduced across the winding of the stator can be increased to therebyintensity the rotor magnetic poles. Accordingly, in the practice of thepresent invention, to secure the required induced voltage, neither isthe volume of the permanent magnets increased, nor the permanent magnetshaving a high residual magnetic flux density are required such asrequired in the prior art, thus making it possible to provide ahigh-performance and inexpensive self-starting synchronous motor havinga required out-of-step torque and a high efficiency.

[0014] Preferably, the distance between the slots in the rotor iron coreand the magnet retaining holes progressively increases from a positionadjacent one end of the rotor magnetic poles towards a position adjacentthe center point of the rotor magnetic poles.

[0015] The present invention according to a third aspect thereofprovides a synchronous motor which comprises a stator including a statoriron core having two-pole windings wound therearound, said stator ironcore having an inner cylindrical surface; a rotor including a rotor ironcore and rotatably accommodated while facing the inner cylindricalsurface of the stator iron core, said rotor including a plurality ofconductor bars positioned adjacent an outer periphery of the rotor ironcore, and shortcircuit rings positioned at axially opposite ends of therotor iron core, said conductor bars and shortcircuit rings beingintegrally molded together by means of an aluminum die casting to form astarter squirrel cage conductor, said rotor having a plurality of magnetretaining slots defined therein at a location on the inner side of theconductor bars; and permanent magnets embedded within the magnetretaining holes in the rotor and defining two magnetic poles ofdifferent polarities. In this synchronous motor, the shortcircuit ringshave an inner diameter positioned outside the associated magnetretaining holes, the inner diameter of the shortcircuit rings at alocation adjacent one end of the magnetic poles being chosen to begreater than an inner diametric dimension at a location adjacent thecenter point of the magnetic poles.

[0016] According to this structure, the width of the permanent magnetscan be increased and, therefore, with no need to increase the axiallength of the permanent magnets, the requires area of surface of themagnetic poles of the permanent magnets can be secured. Accordingly,there is no need to laminate thickness of the rotor iron core, therebydecreasing the cost.

[0017] The inner diameter of the shortcircuit rings on one side wherethe permanent magnets are inserted may lie outside the magnet retainingholes in the rotor iron core, in which case the inner diametricdimension of one of the shortcircuit rings adjacent one end of themagnetic poles is chosen to be greater than the inner diametricdimension thereof adjacent the center point of the magnetic poles, andthe inner diametric dimension of the other of the shortcircuit ringslies inwardly of the whole or a part of the magnet retaining holes. Inthis structure, an end plate made of a non-magnetizable plate ispreferably positioned between such other shortcircuit ring and the rotoriron core so as to cover the magnet retaining holes.

[0018] This is particularly advantageous in that not only is there noneed to increase the laminate thickness of the rotor iron, but also thecross-section of the other shortcircuit ring is increased to reduce theresistance, and therefore, the number of revolution of the motor at thetime of a maximum torque can increase during a period the motorsubsequent to the start thereof attains a synchronous speed, therebyincreasing the starting performance of the motor.

[0019] Also preferably, the inner diameter of the shortcircuit rings onone side where the permanent magnets are inserted lies outside themagnet retaining holes in the rotor iron core, and the inner diametricdimension of one of the shortcircuit rings adjacent one end of themagnetic poles is chosen to be greater than the inner diametricdimension thereof adjacent the center point of the magnetic poles,whereas the inner diametric dimension of the other of the shortcircuitrings lies inwardly of the whole or a part of the magnet retainingholes. In such case, however, one or a plurality of electromagneticsteel plates of the rotor iron core adjacent the other shortcircuit ringis or are not formed with the magnet retaining holes.

[0020] The inner diameter of the shortcircuit rings on one side wherethe permanent magnets are inserted may be of a shape lying along themagnet retaining holes in the rotor iron core.

[0021] Where the stator iron core is made up of a stator laminate ofelectromagnetic steel plates and the rotor iron core is also made up ofa rotor laminate of electromagnetic steel plates, the stator laminatehas a thickness about equal to that of the rotor laminate.

[0022] The present invention in a fourth aspect thereof provides asynchronous motor which comprises a stator including a stator iron corehaving a winding wound therearound and also having an inner cylindricalsurface; a rotor including a rotor iron core in the form of a rotorlaminate of a plurality of electromagnetic steel plates and rotatablyaccommodated while facing the inner cylindrical surface of the statoriron core, said rotor iron core including a magnet retaining portionprovided with magnet retaining slots, a magnetic flux shortcircuitpreventive portion coupled with the magnet retaining portion andprovided with magnetic flux shortcircuit preventive holes communicatedwith the magnet retaining holes, and a rotor outer end portion coupledwith the magnetic flux shortcircuit preventive portion and provided withholes communicated with the magnetic flux shortcircuit preventive holes;and permanent magnets embedded within the magnet retaining holes in therotor and defining rotor magnetic poles. In this structure, the magneticflux shortcircuit preventive holes are smaller than the magnet retainingholes such that by allowing the permanent magnets to be held inengagement with outer edges of the magnetic flux shortcircuit preventiveholes, the permanent magnets are axially positioned.

[0023] This structure is advantageous in that the axial position of thepermanent magnets can be determined relying only on the rotor iron coreand, accordingly, the cost required for assemblage and component partscan be reduced.

[0024] The present invention in a fifth aspect thereof provides asynchronous motor which comprises a stator including a stator iron corehaving a winding wound therearound, said stator iron core having aninner cylindrical surface; a rotor including a rotor iron core in theform of a rotor laminate of a plurality of iron plates and rotatablyaccommodated while facing the inner cylindrical surface of the statoriron core, said rotor iron core including a magnet retaining portionprovided with magnet retaining slots, and a permanent magnet supportportion coupled with the magnet retaining portion and closing the magnetretaining holes; and permanent magnets embedded within the magnetretaining holes, in the rotor and defining rotor magnetic poles. Thepermanent magnets being axially positioned by means of the permanentmagnet support portion.

[0025] This structure is advantageous in that the axial position of thepermanent magnets can be determined relying only on the rotor iron coreand, since one ends of the magnet retaining holes can be closed by therotor iron plate, closure of the magnet retaining hole by means of theend plate secured to the opposite ends of the magnet retaining holes iseffective to permit the use of only one end plate to close the oppositeends of the magnet retaining holes.

[0026] An outer end of the rotor iron core may be coupled with thepermanent magnet support portion and provided with hole positionedaxially of the magnet retaining holes. In this case, the magneticresistance of a magnetic circuit between the N and S poles at theaxially opposite ends of the permanent magnets can be increased toreduce the leakage of the magnetic fluxes, resulting in increase of themotor characteristic.

[0027] Preferably, a starter squirrel cage conductor in the rotor ironcore may be employed in the synchronous motor according to the fifthaspect of the present invention.

[0028] The present invention in a sixth aspect thereof provides asynchronous motor which comprises a stator including a stator iron corehaving a winding wound therearound, said stator iron core having aninner cylindrical surface; a rotor including a rotor iron core androtatably accommodated while facing the inner cylindrical surface of thestator iron core, said rotor including a plurality of conductor barspositioned adjacent an outer periphery of the rotor iron core andshortcircuit rings positioned at axially opposite ends of the rotor ironcore, said conductor bars and said shortcircuit rings being integrallymolded together by means of an aluminum die casting to form a startersquirrel cage conductor, said rotor iron core having a plurality ofmagnet retaining holes defined therein; and permanent magnets embeddedwithin the magnet retaining holes at a location on the inner side of theconductor bars, said magnet retaining holes having a width in a radialdirection of the rotor iron core being greater at a location inwardly ofan axial direction of the rotor than at a location adjacent one end ofthe axial direction of the rotor.

[0029] According to this structure, even though shrinkage stressesgenerated as the shortcircuit rings after the aluminum die casting coolswhile undergoing shrinkage act on the ends of the rotor iron core, thegap between the permanent magnets and the magnet retaining holes can bemaintained at a proper value and, therefore, the insertion of thepermanent magnets into the magnet retaining holes can easily beattained, thereby securing a high-performance motor characteristics.

[0030] Where the width of the magnet retaining holes in the radialdirection is smaller at opposite ends of the axial direction of therotor than at a location inwardly of the axial direction of the rotorand further comprising an electromagnetic steel plate provided outsideone of the opposite ends of the axial direction of the rotor for closingthe magnet retaining holes, the use of only one end plate is sufficientand, therefore, the cost required for the end plate and the number ofassembling steps can advantageously be reduced.

[0031] Also, where the width of the magnet retaining holes in the radialdirection is greater at one of opposite ends of the axial direction ofthe rotor than at a location inwardly of the axial direction of therotor and wherein the other of the opposite ends of the axial directionof the rotor is not provided with any magnet retaining holes for closingthe magnet retaining holes at a location inwardly of the axial directionof the rotor, not only is the use of only one end plate sufficient, butalso the number of combinations of the electromagnetic steel plates isminimized to form the rotor iron core, thereby facilitating manufactureof the motor having a high-performance

[0032] The present invention in a seventh aspect thereof provides asynchronous motor which comprises a stator including a stator iron corehaving a winding wound therearound, said stator iron core having aninner cylindrical surface; a rotor including a rotor iron core androtatably accommodated while facing the inner cylindrical surface of thestator iron core, said rotor including a plurality of conductor barspositioned adjacent an outer periphery of the rotor iron core andshortcircuit rings positioned at axially opposite ends of the rotor ironcore, said conductor bars and said shortcircuit rings being integrallymolded together by means of an aluminum die casting to form a startersquirrel cage conductor, said rotor iron core having a plurality ofmagnet retaining holes defined therein; and permanent magnets embeddedwithin the magnet retaining holes at a location on the inner side of theconductor bars. The rotor iron core employed is in the form of alaminate of electromagnetic steel plates and including an entwiningportion provided adjacent the magnet retaining holes for lamination ofthe electromagnetic steel plates, and the magnet retaining holesadjacent the entwining portion has a width in a radial direction thereofwhich is partially enlarged in a direction towards the entwiningportion.

[0033] According to this structure, even though when the entwiningportion is formed by the use of any known press work, portions of theelectromagnetic steel plates adjacent the entwining portion protrudeunder the influence of press stresses, the gap between the permanentmagnets and the magnet retaining holes can be maintained at a propervalue to thereby facilitate insertion of the permanent magnets and alsoto provide a high-performance motor characteristic.

[0034] The present invention in an eight aspect thereof provides asynchronous motor which comprises a stator including a stator iron corehaving a winding wound therearound, said stator iron core having aninner cylindrical surface; a rotor including a rotor iron core androtatably accommodated while facing the inner cylindrical surface of thestator iron core, said rotor including a plurality of conductor barspositioned adjacent an outer periphery of the rotor iron core andshortcircuit rings positioned at axially opposite ends of the rotor ironcore, said conductor bars and said shortcircuit rings being integrallymolded together by means of an aluminum die casting to form a startersquirrel cage conductor, said rotor iron core having a plurality ofmagnet retaining holes defined therein; and permanent magnets embeddedwithin the magnet retaining holes at a location on the inner side of theconductor bars. The rotor iron core has conductor bar holes definedtherein in an axial direction thereof and positioned inwardly of themagnet retaining holes, and the conductor bar holes are filled up by thealuminum die casting simultaneously with the starter squirrel cageconductor. The conductor bars so filled protrude a distance outwardlyfrom an axial end of the rotor iron core to form respective projectionsfor securement of an end plate. The end plate is made of anon-magnetizable material and secured fixedly to the end of the rotoriron core.

[0035] This structure is effective in that after the starter squirrelcage conductor and the projections for securement of the end plate havebeen formed simultaneously by the use of the aluminum die castingtechnique, engaging the projections into the engagement holes in the endplate and staking or crimping respective tips of the projections resultin firm connection of the end plate to the end face of the rotor ironcore and, therefore, with no need to employ any bolts, the end plate caneasily be secured to the end of the rotor iron core. This permitsreduction in cost for material and facilitates assemblage of the motor.

[0036] The end plate disposed at the axial end of the rotor iron coremay be partly or wholly covered by the corresponding shortcircuit ring,in which case a job of connecting the end plate to the end face of therotor iron core is sufficient at only one side of the rotor iron core.

[0037] The end plate covered by the shortcircuit ring may be providedwith projections engageable in respective holes in the rotor iron core,so that positioning of the end plate can easily be performed and, also,the possibility can be eliminated-which the end plate may displace fromthe right position under the influence of flow of a high-pressurealuminum melt during the aluminum die casting.

[0038] Also, one or a plurality of electromagnetic steel plates at oneaxial end of the rotor iron core may not be provided with any magnetretaining hole, in which case only one end plate is sufficient at theopposite axial end of the rotor iron core, thereby reducing the cost formaterial and the number of assembling steps.

[0039] In addition, projections may be provided at a location where theelectromagnetic steel plates not provided with any magnet retainingholes contact the permanent magnets, so as to protrude towards thepermanent magnets. In this case, the permanent magnets can be axiallypositioned upon engagement only with the projections and, therefore, themagnetic flux shortcircuit between the different poles of the permanentmagnets through the electromagnetic steel plates can be reducedconsiderably, thereby increasing the performance of the motor.

[0040] The present invention in a ninth aspect thereof provides asynchronous motor which comprises a stator including a stator iron corehaving a winding wound therearound, said stator iron core having aninner cylindrical surface; a rotor including a rotor iron core androtatably accommodated while facing the inner cylindrical surface of thestator iron core, said rotor including a plurality of conductor barspositioned adjacent an outer periphery of the rotor iron core andshortcircuit rings positioned at axially opposite ends of the rotor ironcore, said conductor bars and said shortcircuit rings being integrallymolded together by means of an aluminum die casting to form a startersquirrel cage conductor, said rotor iron core having a plurality ofmagnet retaining holes defined therein, one of the shortcircuit ringshaving an inner periphery formed with recesses; permanent magnetsembedded within the magnet retaining holes at a location on the innerside of the conductor bars; and an end plate made of a non-magnetizablematerial and having an outer periphery formed with projectionscomplemental in shape to the recesses in the shortcircuit ring, aperipheral portion of each of the recesses in the shortcircuit ringbeing axially pressed to deform to thereby secure the end plate to anaxial end of the rotor iron core with the projections in the end platereceived in the corresponding recesses in the shortcircuit ring.

[0041] Thus, after the end plate can be mounted on the shortcircuitrings with the projections aligned with and received in thecorresponding recess in the shortcircuit rings, pressing the respectiveperipheral portions of the recesses in the shortcircuit rings to deformresults in fixing of the end plate to the end face of the rotor ironcore, thereby facilitating the fitting of the end plate.

[0042] The present invention according to a tenth aspect thereofprovides a synchronous motor which comprises a stator including a statoriron core having a winding wound therearound, said stator iron corehaving an inner cylindrical surface; a rotor including a rotor iron coreand rotatably accommodated while facing the inner cylindrical surface ofthe stator iron core, said rotor including a plurality of conductor barspositioned adjacent an outer periphery of the rotor iron core andshortcircuit rings positioned at axially opposite ends of the rotor ironcore, said conductor bars and said shortcircuit rings being integrallymolded together by means of an aluminum die casting to form a startersquirrel cage conductor, said rotor iron core having a plurality ofmagnet retaining holes defined therein, one of the shortcircuit ringshaving an inner periphery formed with recesses; permanent magnetsembedded within the magnet retaining holes at a location on the innerside of the conductor bars; said magnet retaining holes being of adesign allowing the permanent magnets, when embedded therein so as to bebutted end-to-end in a generally V-shaped configuration to form a singlemagnetic pole, and having an air space defined between one end face ofthe permanent magnet and an inner face of one end of the magnetretaining hole for preventing shortcircuit of magnetic fluxes, a barrierslot for preventing shortcircuit of magnetic fluxes being definedbetween the magnet retaining holes for accommodating the neighboringpermanent magnets of different polarities, a first bridge portion beingprovided between the magnet retaining hole and the barrier slot so as tosandwich the barrier slot, and a second bridge portion being providedbetween the neighboring permanent magnets of the same polarity and thecorresponding magnet retaining holes, said second bridge portion beingnarrow at a location adjacent a center of the rotor and large at alocation adjacent an outer periphery of the rotor.

[0043] This structure is effective not only to avoid shortcircuit of themagnetic fluxes between the different poles at the end faces of thepermanent magnets to thereby increase the motor performance, but also toreduce the shrinkage strain of the rotor iron core outer diameter at thecenter of the rotor magnetic poles, that have resulted from shrinkage ofthe shortcircuit rings in a radial direction thereof after the aluminumdie casting, to a very small value because of the strength of the bridgeportion having been-increased. Therefore, the gap size between thestator iron core inner diameter and the rotor iron core outer diametercan be accurately obtained merely by blanking the electromagnetic steelplates for the rotor iron core by the use of any known press work andthe outer diameter of the rotor iron core need not be ground, therebyreducing the number of assembling steps.

[0044] The present invention according to an eleventh aspect thereofprovides a synchronous motor which comprises a stator including a statoriron core having a winding wound therearound, said stator iron corehaving an inner cylindrical surface; a rotor including a rotor iron coreand rotatably accommodated while facing the inner cylindrical surface ofthe stator iron core, said rotor including a plurality of conductor barspositioned adjacent an outer periphery of the rotor iron core andshortcircuit rings positioned at axially opposite ends of the rotor ironcore, said conductor bars and said shortcircuit rings being integrallymolded together by means of an aluminum die casting to form a startersquirrel cage conductor, said rotor iron core having a plurality ofmagnet retaining holes defined therein, one of the shortcircuit ringshaving an inner periphery formed with recesses; permanent magnetsembedded within the magnet retaining holes at a location on the innerside of the conductor bars to provide two magnetic poles; said rotoriron core increasing from axially opposite ends thereof towards a centerpoint of the length of the rotor to render it to represent a generallyoval shape, the permanent magnets being mounted after formation of thestarter squirrel cage conductor by means of the aluminum die casting.

[0045] According to this structure, even if the shrinkage strain of therotor iron core outer diameter in a radial direction increases towardsthe center of the rotor magnetic poles after the aluminum die casting,the outer diameter of the rotor iron core after shrinkage can be kept tothe right round shape and, therefore, the gap size between the statoriron core inner diameter and the rotor iron core outer diameter can beaccurately obtained merely by blanking the electromagnetic steel platesfor the rotor iron core by the use of any known press work and the outerdiameter of the rotor iron core need not be ground, thereby reducing thenumber of assembling steps. Also, since the aluminum die casting isperformed while the permanent magnets and the end plates have not yetbeen fitted, the job can easily be performed without incurring anydefective component parts, thereby increasing the productivity.

[0046] Where the permanent magnets are employed in the form of a rareearth magnet, a strong magnetic force can be obtained and both the rotorand the motor itself can advantageously manufactured in a compact sizeand lightweight.

BRIEF DESCRIPTION OF DRAWINGS

[0047] The present invention will become readily understood from thefollowing description of preferred embodiments thereof made withreference to the accompanying drawings, in which like parts aredesignated by like reference numerals and in which:

[0048]FIG. 1 is a transverse sectional view of a rotor used in asynchronous motor according to a first preferred embodiment of thepresent invention;

[0049]FIG. 2 is a chart showing a pattern of distribution of magneticflux densities in a gap between a stator and the rotor;

[0050]FIG. 3 is a transverse sectional view of the rotor used in thesynchronous motor according to a second preferred embodiment of thepresent invention;

[0051]FIG. 4 is a transverse sectional view of the rotor used in thesynchronous motor according to a third preferred embodiment of thepresent invention;

[0052]FIG. 5 is a transverse sectional view of the rotor used in thesynchronous motor according to a fourth preferred embodiment of thepresent invention;

[0053]FIG. 6 is a transverse sectional view of the rotor used in theprior art self-starting synchronous motor of a kind utilizing permanentmagnets;

[0054]FIG. 7 is a chart showing the prior art self-starting synchronousmotor exhibiting a pattern of distribution of magnetic flux densities inthe gap between the stator and the rotor, which pattern represents arectangular waveform;

[0055]FIG. 8 is a chart showing the magnetic flux density distributionpattern representing a generally trapezoidal waveform;

[0056]FIG. 9 is a chart showing the relation between the magnetic fluxamount and time that is exhibited when the magnetic flux densitydistribution pattern represents the rectangular waveform;

[0057]FIG. 10 is a chart showing the relation between the magnetic fluxamount and time that is exhibited when the magnetic flux densitydistribution pattern represents the trapezoidal waveform;

[0058]FIG. 11 is a chart showing the relation between the inducedvoltage and time that is exhibited when the magnetic flux densitydistribution pattern represents the rectangular waveform;

[0059]FIG. 12 is a chart showing the relation between the inducedvoltage and time that is exhibited when the magnetic flux densitydistribution pattern represents the trapezoidal waveform;

[0060]FIG. 13 is a chart showing the induced voltage versus angle α thatis exhibited when the magnetic flux density distribution patternrepresents the trapezoidal waveform;

[0061]FIG. 14 is a longitudinal sectional view of a self-startingsynchronous motor of a type-utilizing permanent magnets according to afifth preferred embodiment of the present invention;

[0062]FIG. 15 is a transverse sectional view of the rotor used in thesynchronous motor shown in FIG. 14;

[0063]FIG. 16 is a plan view of an end plate of the rotor;

[0064]FIG. 17 is an end view of the rotor;

[0065]FIG. 18 is a longitudinal sectional view of the self-startingpermanent magnet synchronous motor according to a sixth preferredembodiment of the present invention;

[0066]FIG. 19 is an end view of the rotor used in the synchronous motorof FIG. 18;

[0067]FIG. 20 is a longitudinal sectional view of the self-startingpermanent magnet synchronous motor according to a seventh preferredembodiment of the present invention;

[0068]FIG. 21 is an end view of an electromagnetic steel plate at oneend of a rotor iron core employed in the synchronous motor of FIG. 20;

[0069]FIG. 22 is an end view of the rotor used in the synchronous motorof FIG. 20;

[0070]FIG. 23 is an end view of the rotor used in the self-startingpermanent magnet synchronous motor according to an eighth preferredembodiment of the present invention;

[0071]FIG. 24 is a longitudinal sectional view of the self-startingpermanent magnet synchronous motor according to a ninth preferredembodiment of the present invention;

[0072]FIG. 25 is a transverse sectional view of the prior art rotor;

[0073]FIG. 26 is a longitudinal sectional view of the rotor used in thesynchronous motor according to a tenth preferred embodiment of thepresent invention;

[0074]FIG. 27 is a plan view of a rotor iron plate E;

[0075]FIG. 28 is a plan view of a rotor iron plate F;

[0076]FIG. 29 is a longitudinal sectional view of the rotor used in thesynchronous motor according to an eleventh preferred embodiment of thepresent invention;

[0077]FIG. 30 is a plan view of the rotor iron plate G;

[0078]FIG. 31 is a longitudinal sectional view of the rotor used in thesynchronous motor according to a twelfth preferred embodiment of thepresent invention;

[0079]FIG. 32 is a longitudinal sectional view of the rotor used in thesynchronous motor according to a thirteenth preferred embodiment of thepresent invention;

[0080]FIG. 33 is a plan view of the rotor iron plate H;

[0081]FIG. 34 is a plan view of the rotor iron plate I;

[0082]FIG. 35 is a longitudinal sectional view of the rotor used in theself-starting permanent magnet synchronous motor according to afourteenth preferred embodiment of the present invention;

[0083]FIG. 36 is a plan view of the electromagnetic steel plate J in therotor iron core employed in the synchronous motor of FIG. 35;

[0084]FIG. 37 is a plan view of the electromagnetic steel plate K atopposite ends of the rotor iron core employed in the synchronous motorof FIG. 35;

[0085]FIG. 38 is a longitudinal sectional view of the rotor used in theself-starting synchronous motor of the type employing the permanentmagnets according to a fifteenth preferred embodiment of the presentinvention;

[0086]FIG. 39 is a plan view of the electromagnetic steel plate L at oneend face of the rotor iron core used in the synchronous motor of FIG.38;

[0087]FIG. 40 is a longitudinal sectional view of the rotor employed inthe self-starting permanent magnet synchronous motor according to asixteenth preferred embodiment of the present invention;

[0088]FIG. 41 is a longitudinal sectional view of the rotor employed inthe self-starting permanent magnet synchronous motor according to aseventeenth preferred embodiment of the present invention;

[0089]FIG. 42 is an end view of the synchronous motor shown in FIG. 41;

[0090]FIG. 43 is a plan view of the electromagnetic steel plate of therotor used in the self-starting permanent magnet synchronous motoraccording to an eighteenth preferred embodiment of the presentinvention;

[0091]FIG. 44 is a fragmentary enlarged sectional view of an entwiningportion as viewed in a direction conforming to the direction oflamination in the synchronous motor of FIG. 43;

[0092]FIG. 45 is a longitudinal sectional view of the self-startingpermanent magnet synchronous motor according to a nineteenth preferredembodiment of the present invention;

[0093]FIG. 46 is a transverse sectional view of the rotor used in thesynchronous motor shown in FIG. 45;

[0094]FIG. 47 is a plan view of the end plate used in the synchronousmotor shown in FIG. 45;

[0095]FIG. 48 is a longitudinal sectional view of the self-startingpermanent magnet synchronous motor according to a twentieth preferredembodiment of the present invention;

[0096]FIG. 49 is a plan view of the end plate used in the synchronousmotor shown in FIG. 48;

[0097]FIG. 50 is a cross-sectional view taken along the line C-C′ inFIG. 49;

[0098]FIG. 51 is longitudinal sectional view of the self-startingpermanent magnet synchronous motor according to a twenty-first preferredembodiment of the present invention;

[0099]FIG. 52 is a plan view of the electromagnetic steel plate at theend of the rotor iron core employed in the synchronous motor shown inFIG. 51;

[0100]FIG. 53 is a plan view of the electromagnetic steel plate at theend of the rotor iron core employed in the self-starting synchronousmotor according to a twenty-second preferred embodiment of the presentinvention;

[0101]FIG. 54 is a fragmentary enlarged longitudinal sectional view ofthe rotor employed in the synchronous motor shown in FIG. 53;

[0102]FIG. 55 is a longitudinal sectional view of the self-startingpermanent magnet synchronous motor according to a twenty-third preferredembodiment of the present invention,

[0103]FIG. 56 is a longitudinal sectional view of the synchronous motorbefore the end plate is fixed;

[0104]FIG. 57 is an end view of the synchronous motor of FIG. 56;

[0105]FIG. 58 is a longitudinal sectional view of the prior art rotor;

[0106]FIG. 59 is a cross-sectional view taken along the line A-A′ inFIG. 58;

[0107]FIG. 60 is a longitudinal sectional view of the rotor used in theself-starting permanent magnet synchronous motor according to atwenty-fourth preferred embodiment of the present invention,

[0108]FIG. 61 is a transverse sectional view of the rotor shown in FIG.60;

[0109]FIG. 62 is a fragmentary enlarged view showing a bridge portion;and

[0110]FIG. 63 is a plan view of the electromagnetic steel plate of therotor used in the self-starting permanent magnet synchronous motoraccording to a twenty-fifth preferred embodiment of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0111] First Embodiment (FIGS. 1 and 2)

[0112]FIG. 1 illustrates a transverse sectional view of a rotor used ina self-starting synchronous motor of a type utilizing permanent magnetsaccording to a first preferred embodiment of the present invention. Inthis figure, reference numeral 21 represents a rotor, and referencenumeral 22 represents a rotor iron core. The rotor iron core 22 has aplurality of slots 23 defined in an outer peripheral portion thereof foraccommodating a corresponding number of conductor bars 24, which areintegrally molded together with shortcircuit rings (not shown) ataxially spaced opposite ends of the rotor iron core 22 by the use of anyknown aluminum die casting to thereby provide a starter squirrel cageconductor. Permanent magnets 26 are embedded in respective magnetretaining holes defined in the rotor iron core 23 at a location radiallyinwardly of a round row of the conductor bars 24.

[0113] So far shown in FIG. 1, two plate-like permanent magnets 26 arebutted end-to-end in a generally V-shaped configuration to form a singlerotor magnetic pole and, since four permanent magnets are employed inthe rotor, two rotor magnetic poles are formed. Reference characters T2and T3 represents the interval between the neighboring slots 23positioned adjacent the rotor magnetic poles defined by the permanentmagnets, and reference character T4 represents the interval between theneighboring slots 23 positioned adjacent a center point between therotor magnetic poles. In the illustrated embodiment, the intervals T2and T3 are chosen to be smaller than the interval T4.

[0114]FIG. 2 is a chart showing a pattern of distribution of magneticflux densities in an air gap between the rotor and the stator, whereinthe axis of ordinates represents the magnetic flux density B and theaxis of abscissas represents the angle θ of the air gap in a directionconforming to the direction of rotation of the rotor with the originrepresented by the center point between the rotor magnetic pole. Sinceat a position adjacent the ends of the rotor magnetic poles theintervals T2 and T3 are smaller than the interval T4 at the centerpoints of the rotor magnetic poles, magnetic fluxes emanating from thepermanent magnets 26 do hardly leak to the outer peripheral surface ofthe rotor 21 and, instead, leak to the outer peripheral surface adjacentthe center points of the rotor magnetic poles. For this reason, thepattern of distribution of the magnetic flux densities in the air gapbetween the stator and the rotor 21 represents a generally trapezoidalwaveform or a generally sinusoidal waveform and, since as compared witha rectangular waveform the amount of change of the magnetic fluxes perunitary time increases, it is possible to increase the voltage inducedacross the winding of the stator.

[0115] In contrast thereto, in the prior art self-starting permanentmagnet synchronous motor, the slots in the rotor iron core arecircumferentially spaced at regular intervals and have the same radiallengths as measured in a direction radially of the rotor iron core and,therefore, the pattern of distribution of the magnetic flux densitiestends to represents a rectangular waveform. In general, the intensity ofthe rotor magnetic poles brought about by the permanent magnets can berelatively grasped by measuring the magnitude of the voltage inducedacross the winding of the stator when the rotor is externally rotatedwhile no voltage is applied to the motor.

[0116] The relation between the shape of the pattern of distribution ofthe magnetic flux densities in the air gap between the stator and therotor and the voltage induced across the stator winding by the action ofthe rotor magnetic poles will now be discussed as applied to thetwo-pole self-starting motor of the type utilizing the permanentmagnets.

[0117] The case in which the pattern Bg(θ) of distribution of themagnetic flux densities in the air gap represents a rectangular waveformBg1(θ) is shown in FIG. 7, and the case In which the pattern ofdistribution of the magnetic flux densities in the air gap represents agenerally trapezoidal waveform Bg2(θ) is shown in FIG. 8. The axis ofabscissas represents the angle θ of the air gap in a directionconforming to the direction of rotation with the point of originrepresented by the center point between the rotor magnetic poles. InFIG. 7, Bg1m represents a maximum value of Bg1(θ) that can be expressedby the following equations:

Bg1(θ)=Bg1m(when 0≦θ≦π)  (1)

Bg1(θ)=−Bg1m(when π≦θ≦2)(2)

[0118] In FIG. 8, Bg2m represents a maximum value of Bg2(θ) that can beexpressed by the following equations if the angle α of inclination ofBg2(θ) from θ=0.

Bg2(θ)=θtan α (when 0≦θ≦Bg2m/tan α)  (3)

Bg2(θ)=Bg2m (when Bg2m/tan α≦θ≦π−B2m/tanα)  (4)

B2(θ)=−θtanα+πtan α(when π−Bg2m/tanα≦θπ)  (5)

[0119] It is assumed that the magnetic fluxes of the permanent magnetswill nor be shortcircuited within the rotor and are all flow through thestator iron core. Accordingly, regardless of the shape of the waveformof the pattern of distribution of the magnetic flux densities the airgap the amount of the magnetic fluxes flowing in the stator is constantand the area of surface of the waveform for each magnetic pole remainsthe same as can be expressed by the following equation:

B _(g1m) π=B _(g2m)[π−(B _(g2m)/tanα)]  (6)

[0120] Although the stator winding is distributed over a regioncorresponding to one magnetic pole, the stator winding can be arrangedintensively in a width of an angle rr in a direction conforming to thedirection of rotation corresponding to the single magnetic pole and thenumber of turns thereof assumed to be n. The amount of the magneticfluxes φ passing through the winding during rotation of the rotormagnetic poles at an angular velocity w(t) can be expressed by thefollowing equation: $\begin{matrix}{{\varphi (t)} = {\int_{\omega \quad t}^{{\omega \quad t} + \pi}{{B_{g}(\theta)}{\theta}}}} & (7)\end{matrix}$

[0121] The amount of the magnetic fluxes φ1(t) in the case where thepattern Bg(θ) of distribution of the magnetic flux densities in the airgap represents the rectangular waveform Bg1(θ) represents such awaveform as shown in FIG. 9 when Bg1(θ) of each of the equations (1) and(2) is substituted for Bg(θ) in the equation (7). The amount of themagnetic fluxed φ2(t) in the case of the trapezoidal waveform Bg2(θ)represents such a waveform as shown in FIG. 10 when Bg1(θ) in each ofthe equations (4) and (5) is substituted for Bg(θ) in the equation (7).The axis of ordinates and the axis of abscissas in each of FIGS. 9 and10 represent the amount of the magnetic fluxes φ and the time t,respectively.

[0122] The waveform V(t) of the voltage induced across the statorwinding can be expressed by the following equation: $\begin{matrix}{{V(t)} = {{{- n}\frac{}{t}{\int_{\omega \quad t}^{{\omega \quad t} + \pi}{{B_{g}(\theta)}{\theta}}}} = {{- \omega}\quad {n\left\lbrack {{B\left( {\theta + \pi} \right)} - {B(\theta)}} \right\rbrack}}}} & (8)\end{matrix}$

[0123] The waveform V1(t) of the induced voltage in the case where thepattern of distribution of the magnetic flux densities in the air gaprepresents the rectangular waveform Bg1(θ) and the waveform V2(t) of theinduced voltage in the case where the pattern of distribution of themagnetic flux densities in the air gap represents the trapezoidalwaveform Bg2(θ) are shown in FIGS. 11 and 12, respectively, in which theaxis of ordinates represents the induced voltage V(t) and the axis ofabscissas represents the time t.

[0124] The induced voltage V means an effective value of the inducedvoltage waveform and is expressed by the following equation:$\begin{matrix}{V = \sqrt{\frac{1}{\pi}{\int_{0}^{\pi}{{V^{2}(t)}{t}}}}} & (9)\end{matrix}$

[0125] Substituting the equation (8) for the equation (9) results in theinduced voltage V that is expressed by the following equation (10):$\begin{matrix}{V = \sqrt{\frac{\omega^{2}n^{2}}{\pi}{\int_{0}^{\pi}{\left\lbrack {{B\left( {\theta + \pi} \right)} - {B(\theta)}} \right\rbrack^{2}{\theta}}}}} & (10)\end{matrix}$

[0126] The induced voltage V₁ in the case where the pattern ofdistribution of the magnetic flux densities in the air gap representsthe rectangular waveform Bg1(θ) can be expressed by the followingequation by substituting the equations (1) and (2) for the equation(10): $\begin{matrix}{V_{1} = {2\omega \quad n\quad B_{g2m}\sqrt{1 - \frac{4B_{g2m}}{3{\pi tan}\quad \alpha}}}} & (11)\end{matrix}$

[0127] The induced voltage V₂ in the case where the pattern ofdistribution of the magnetic flux densities in the air gap representsthe trapezoidal waveform Bg2(θ) can be expressed by the followingequation by substituting the equations (3) and (4) for the equation(10): $\begin{matrix}{V_{2} = {2\omega \quad n\quad B_{g2m}\sqrt{1 - \frac{4B_{g2m}}{3{\pi tan}\quad \alpha}}}} & (12)\end{matrix}$

[0128] V₂ is a function of the angle α shown in FIG. 8 and is shown inFIG. 13. When α=π/2, V₂ takes the same value as the equation (11) and itmay be said that when α=π/2 in FIG. 13 the pattern of distribution ofthe magnetic flux densities in the air gap represents the inducedvoltage of the rectangular waveform. From FIG. 8, since the a is smallerthan π/2 where the pattern of distribution of the magnetic fluxdensities in the air gap represents the trapezoidal waveform, it willreadily be seen from FIG. 13 that the induced voltage where the patternof distribution of the magnetic flux densities in the air gap representsthe rectangular waveform is lower than that where the pattern ofdistribution of the magnetic flux densities represents the trapezoidalwaveform.

[0129] The induced voltage where the pattern of distribution of themagnetic flux densities represents the sinusoidal waveform can besimilarly expressed by the equation (9), and it can be said that theinduced voltage where the pattern of distribution of the magnetic fluxdensities in the air gap represents the rectangular waveform is lowerthan that where the pattern of distribution of the magnetic fluxdensities represents the sinusoidal waveform. Accordingly, where thepattern of distribution of the magnetic flux densities represents therectangular waveform, the out-of-step torque is reduced due to the factthat the rotor magnetic poles are weak and the efficiency will decreasebecause of increase of the electric current flowing through the statorwinding. Therefore, to secure the required induced voltage, it isnecessary to increase the size of the permanent magnets or to employpermanent magnets having a high residual magnetic flux density and,therefore, there has been a problem in that the cost for the permanentmagnets is high, accompanied by increase in cost of the motor.

[0130] According to the illustrated embodiment of the present invention,however, the voltage induced across the stator winding can be increasedby rendering the pattern of distribution of the magnetic flux densitiesin the air gap between the stator and the rotor to represent either theapproximately trapezoidal waveform or the approximately sinusoidalwaveform. Therefore, it is possible to provide the high-performance,inexpensive self-starting permanent magnet synchronous motor, with noneed to increase the size of the permanent magnets, nor to employ thepermanent magnets having a high residual magnetic flux density.

[0131] It is to be noted that although in the foregoing embodimentreference is made to the rotor of the synchronous motor employing thetwo poles, the present invention may not be limited thereto and may beequally applied to the rotor having, for example, four or more magneticpoles. Also, although the permanent magnets have been employed in theplate-like form, the present invention is not limited thereto and thepresent invention is equally applicable to the rotor employing permanentmagnets of, for example, an arcuate shape or any other suitable shape.

[0132] Second Embodiment (FIG. 3)

[0133]FIG. 3 illustrates a transverse sectional view of the rotor usedin the self-starting permanent magnet synchronous motor according to asecond preferred embodiment of the present invention. In FIG. 3, therotor 21 is shown as rotating in a direction shown by the arrow. Duringa loaded operation, a composite magnetic flux of the magnetic fluxemanating from the stator winding and the magnetic flux emanating fromthe permanent magnets 26 flows in a larger quantity in a portion 29between the neighboring slots that are located on a leading side offsetθ1 angularly in a direction conforming to the direction of rotation ofthe rotor, than that flowing in a portion 28 between the neighboringslots that are located on a trailing side from the center of the rotormagnetic poles with respect to the direction of rotation of the rotor.The size of that portion 29, that is, the spacing T8 between theneighboring slots on respective sides of that portion 29 is chosen to belarger than the spacing T9 between the neighboring slots on respectivesides of that portion 28 and, therefore, it is possible to avoidmagnetic saturation of the iron core at that portion 29 between theneighboring slots to thereby secure a favorable motor characteristic.

[0134] Third Embodiment (FIG. 4)

[0135]FIG. 4 illustrates a transverse sectional view of the rotor usedin the self-starting permanent magnet synchronous motor according to athird preferred embodiment of the present invention. In FIG. 4, one ofthe slots that is identified by 30 is the slot positioned adjacent thecenter of the rotor magnetic poles, and the slots 31 and 32 arepositioned adjacent one of opposite ends of the rotor magnetic poles.These slots 30, 31 and 32 have different radial lengths H30, H31 andH32, respectively, and the distances Y31 and Y32 between the slot 31 andthe magnet retaining hole 25 and between the slot 32 and the magnetretaining hole 25 are chosen to be so smaller than the distance Y30between the slot 30 and the magnet retaining hole 25 that the magneticfluxes emanating from the permanent magnets will hardly leak to theouter peripheral surface of the rotor adjacent the ends of the rotormagnetic poles and will, instead, leak to the outer peripheral surfaceof the rotor adjacent the center of the rotor magnetic poles. For thisreason, the pattern of distribution of the magnetic flux densities inthe air gap between the stator and the rotor can represent the generallytrapezoidal waveform or the generally sinusoidal waveform and, since theamount of change of the magnetic flux per unitary time is so large ascompared with the rectangular waveform, the voltage induced across thestator winding can be increased. Accordingly, with no need to increasethe volume of the permanent magnets or employ the permanent magnetshaving a high residual magnetic flux density in order to secure therequired induced voltage such as implemented in the prior art, it ispossible to provide the high-performance, inexpensive self-startingsynchronous motor of the type employing the permanent magnets that canexhibit a required out-of-step torque and a high efficiency.

[0136] Fourth Embodiment (FIG. 5)

[0137]FIG. 5 illustrates a transverse sectional view of the rotor usedin the self-starting permanent magnet synchronous motor according to afourth preferred embodiment of the present invention. In FIG. 5, theslots 33, 34, 35, 36, 37, 38 and 39 are those positioned in a regionranging from the center to one end of the rotor magnetic poles and arespaced progressively decreasing distances Y33, Y34, Y35, Y36, Y37, Y38and Y39, respectively, from the magnet retaining hole 35.

[0138] Arrow-headed lines shown in FIG. 5 illustrate the manner in whichthe magnetic fluxes of the magnetic field formed by the stator windingrun across the rotor 1. For simplification purpose, the pattern of flowof the magnetic fluxed is shown only in a lower half of the rotor andnot shown in an upper half of the same. As can be seen from this figure,the amount of the magnetic fluxes from the stator is small at a portionbetween the slot 39 adjacent the end of the rotor magnetic poles and themagnet retaining hole, but increases as the center of the magnetic polesapproaches because the magnetic fluxes flowing in between the slotsoverlap. Thus, at a location adjacent the center of the magnetic poles,the amount of the magnetic fluxes is maximized where the magnetic fluxesof the magnetic field developed by the stator winding are intensified.

[0139] However, since the distance between each of the slots and themagnet retaining hole as well progressively increases from the end ofthe rotor magnetic poles towards the center of the rotor magnetic poles,any possible magnetic saturation of an iron core portion between theslots and the magnet retaining hole can be prevented, thereby ensuring afavorable motor characteristic.

[0140] Fifth Embodiment (FIGS. 4 to 7)

[0141]FIG. 14 is a longitudinal sectional view of the self-startingsynchronous motor of a type utilizing permanent magnets according to afifth preferred embodiment of the present invention, and FIG. 15 is across-sectional view taken along the line A-A′ in FIG. 14. FIG. 16 is aplan view of an end plate made of a non-magnetizable material and usedfor protection of the permanent magnets. FIG. 17 is an end view of therotor after the permanent magnets have been inserted and arranged, butbefore the end plate is fixed to the rotor.

[0142] In these figures, reference numeral 41 represents a rotor, andreference numeral 42 represents a rotor iron core in the form of alaminated structure of electromagnetic steel plates. Reference numeral43 represents conductor bars molded together with shortcircuit rings 44positioned on respective ends of the conductor bars by means of analuminum die casting technique to provide a starter squirrel cageconductor. Reference numeral 45 represents permanent magnets each havinga width Q. Reference numeral 46 represents magnet retaining holesdefined in the rotor iron core 42 for accommodating therein thepermanent magnets. After the aluminum die casting, two plate-likepermanent magnets 45 of the same polarity are butted end-to-end in agenerally V-shaped configuration to form a single rotor magnetic poleand, since four permanent magnets 45 e employed in the rotor, two rotormagnetic poles are formed.

[0143] Reference numeral 47 represents a barrier for preventing ashortcircuit of the magnetic fluxes developed between the neighboringpermanent magnets of different polarities, which is also filled inposition by means of the aluminum die casting. Reference numeral 48represents end plates made of a non-magnetizable material and used toprotect the permanent magnets, each being formed with an engagement hole48 a. Reference numeral 49 represents axial holes defined in the rotoriron core 42 so as to extend axially thereof, which holes are filledwith aluminum 50 that is used during the aluminum die casting to formthe starter squirrel cage conductor. The aluminum 50 filling up theaxial hole 49 protrudes axially outwardly from the opposite ends of therotor iron core 42 to thereby define projections 50 a as best shown inFIG. 14. The end plates 48 are, after the projections 50 a have beenpassed through the associated engagement holes 48 a in the end plates48, fixed to the opposite end faces of the rotor iron core 42 bycrimping or staking the projections 50 a to enlarge as shown by brokenlines in FIG. 14. Reference numeral 51 represents a bearing hole definedin the rotor iron core 42.

[0144] The amount of the magnetic fluxes of the permanent magnets 45that can be obtained from the rotor is substantially proportional to theproduct of the width Q of the permanent magnets 45 times the length ofthe permanent magnets 45 as measured in the axial direction of therotor, that is, the area of magnetic poles of the permanent magnets 45.

[0145] It is to be noted that although in the foregoing description thepermanent magnets which have been magnetized are inserted and arranged,the rotor magnetic poles may be equally formed by inserting andarranging permanent magnets, which have not yet been magnetized, in therotor iron core to complete the rotor and then polarizing the permanentmagnets with the use of a magnetizing apparatus.

[0146] According to the fifth embodiment of the present invention, theangle β of end-to-end abutment of the same poles of the permanentmagnets 45 is chosen to be larger than the angle α in the prior art thatis 90° as shown in FIG. 25, and the width Q of each permanent magnet 45as measured in a direction perpendicular to the longitudinal axisthereof is enlarged to a value larger than the width P in the prior artas shown in FIG. 25. Increase of the angle of end-to-end abutment of thepermanent magnets and selection of the inner radial dimension c at alocation adjacent the end of the rotor magnetic poles to be larger thanthe inner radial dimension b at a location adjacent the center of therotor magnetic poles is effective to allow the permanent magnets of theincreased width to be employed. In correspondence with the increase ofthe angle of end-to-end abutment of the permanent magnets 45 andincrease of the width of the permanent magnets 45, each of theshortcircuit rings 44 employed in the present invention is not round inshape such as used in the prior art, but of a generally rhombic shape,as shown in FIG. 14, having its outer contour positioned outwardly ofthe magnet retaining holes 46 and allowing an inner diameter of the endsof the rotor magnetic poles to be greater than that of the center of therotor magnetic poles.

[0147] The reason that the inner diameter of each of the shortcircuitrings 44 a is not chosen to be round in conformity with the innerdiameter at the end of the magnetic poles of the total peripheral rotoris that, if it is so chosen, the equivalent sectional surface area ofeach shortcircuit ring A as a whole of 44 a will become so excessivelysmall as to increase the resistance, resulting in reduction in startingcapability of the motor.

[0148] As discussed above, according to the fifth embodiment of thepresent invention, since the permanent magnets 45 can have an increasedarea of surface of the magnetic poles, the amount of the magnetic fluxesof the permanent magnets required by the motor can be obtained.

[0149] Sixth Embodiment (FIGS. 18 and 19)

[0150] A sixth preferred embodiment of the present invention will now bedescribed with reference to FIGS. 18 and 19., wherein FIG. 18 is alongitudinal sectional view of the self-starting synchronous motor of atype utilizing permanent magnets according to the sixth embodiment ofthe present invention and FIG. 19 is an end view as viewed from an Sside in FIG. 18. In FIG. 19, broken lines show the position of magnetretaining holes 46 and single-dotted lines show an outer contour of theend plate 58. Although an end view of the rotor as viewed from an R sideis not shown, the width and the angle of end-to-end abutments of thepermanent magnets 45 and the inner diametric shape of the shortcircuitring A of 44 a are all similar to those in the previously describedfirst embodiment of the present invention, and the shortcircuit ring Bof 44 b on the opposite S side has an inner diameter that is round andis so chosen to be small as to allow it to be positioned inwardly of themagnet retaining holes 46.

[0151] Referring to FIGS. 18 and 19, the end plate 58 is similarlyarranged in abutment with an end face of the rotor iron core 42 on the Sside and is of a shape sufficient to encompass the magnet retainingholes 46 and, accordingly, there is no possibility that the die castaluminum may leak into the magnet retaining holes 46 which wouldotherwise render it difficult to insert the permanent magnets 45.

[0152] Seventh Embodiment (FIGS. 20 to 22)

[0153] A seventh preferred embodiment of the present invention will nowbe described with reference to FIGS. 20 to 22. FIG. 20 is a longitudinalsectional view of the self-starting synchronous motor of a typeutilizing permanent magnets according to the seventh embodiment of thepresent invention, FIG. 21 is a plan view of one or a plurality ofelectromagnetic steel plates 59 at one end on the S side of the rotoriron core 2, and FIG. 22 is an end view as viewed from the S side.Although an end view of the rotor as viewed from the R side is notshown, the width and the angle of end-to-end abutments of the permanentmagnets 45 and the inner diametric shape of the shortcircuit ring A of44 a are all similar to those in the previously described fifthembodiment of the present invention.

[0154] Referring to FIGS. 20 to 22, the shortcircuit ring C of 44 c onthe S side has its inner diameter or bore which is round and is sochosen as to be positioned inwardly of the magnet retaining holes 46.One or a plurality of electromagnetic steel plates 59 at the end on theS side of the rotor iron core 42 is provided with slots of the sameshape and size defined at the same position as the electromagnetic steelplates other than those at the end, but no magnetic retaining hole 46 isprovided. Accordingly, even though the inner diameter of theshortcircuit ring C of 44 c is small, there is no possibility that thedie cast aluminum will leak into the magnet retaining holes 46 to renderit to be difficult to insert the permanent magnets.

[0155] Eighth Embodiment (FIG. 23)

[0156] An eighth embodiment of the present invention will be describedwith reference to FIG. 23 which is an end view of the rotor as viewed ina direction conforming to the direction of insertion of permanentmagnets 45, showing the rotor after the permanent magnets 45 have beeninserted and arranged, but before the end plate is mounted.

[0157] Referring to FIG. 23, the inner diameter or bore of theshortcircuit ring D of 44 d is of a shape conforming to and extendingalong the magnet retaining holes 46. This design permits the permanentmagnets 45 to be inserted along a wall surface inside the inner diameteror bore of the shortcircuit ring D of 44 d, thereby facilitating a jobof insertion of the permanent magnets to thereby increase the ease toassembly.

[0158] Ninth Embodiment (FIG. 24)

[0159] A ninth preferred embodiment of the present invention will bedescribed with reference to FIG. 24 and also to FIG. 17 used inconnection with the fifth embodiment of the present invention. FIG. 24illustrates a transverse sectional view of the self-starting synchronousmotor of the type employing the permanent magnets according to the ninthembodiment of the present invention. In this figure, reference numeral61 represents a stator, and reference numeral 62 represents a statoriron core in the form of a laminate structure of electromagnetic steelplates, which laminate structure has a laminate thickness indicated byLs. Reference numeral 63 represents a stator winding wound around thestator iron core 62. The rotor 41 employed therein is substantiallyidentical with that described in connection with the fifth embodimentwith reference to FIG. 17 and are not therefore described for the sakeof brevity however, as is the case with the rotor shown in FIG. 17, byincreasing the width of the permanent magnets 45 as measured in adirection perpendicular to the longitudinal axis thereof to therebyincrease the area of surface of the magnetic poles of the permanentmagnets 45 to increase the amount of the magnetic fluxes emanating fromthe permanent magnets 45, and also by designing the inner diameter orbore of the shortcircuit ring A of 44 a to be positioned outwardly ofthe magnet retaining holes 46 and, again by selecting the inner radialdimension adjacent the end of the rotor magnetic poles of theshortcircuit ring A of 44 a to be larger than that adjacent the centerof the rotor magnetic poles, the laminate thickness of theelectromagnetic steel plates forming the rotor iron core 42 canadvantageously reduced to a value substantially equal to the laminatethickness Ls of the stator iron core.

[0160] The motor of the type utilizing the permanent magnets isgenerally designed by selecting the axial length of the permanentmagnets to be greater than the laminate thickness of the stator ironcore so that portions of the magnetic fluxes of the permanent magnets,which emerge outwardly from the opposite ends of the stator iron core,can flow inwardly of the stator iron core from the opposite ends thereofto thereby increase the amount of the magnetic fluxes that runs throughthe whole of the stator iron core and, for that purpose, the laminatethickness of the rotor iron core is chosen to be greater than thelaminate thickness of the stator iron core. In contrast thereto,according to the ninth embodiment of the present invention, the designhas been employed as hereinabove described to render the laminatethickness Ls of the stator iron core and the laminate thickness L_(R) ofthe rotor iron core to be substantially equal to each other.

[0161] In view of the foregoing, the number of the electromagnetic steelplates for each of the stator and rotor iron cores that aresimultaneously blanked within the same dies is substantially equal forthe both and, therefore, production of surplus electromagnetic steelplates can be suppressed to thereby reduce the cost.

[0162] Tenth Embodiment (FIGS. 26 to 28)

[0163] A tenth preferred embodiment of the present invention will now bedescribed with reference to FIGS. 26 to 28. FIG. 26 is a longitudinalsectional view of the rotor used in the synchronous motor according tothe tenth embodiment of the present invention. In FIG. 26, referencenumeral 71 represents a rotor, and reference numeral 72 represents arotor iron core. Reference numeral 72 a represents a rotor iron coreformed by laminating rotor iron plates E, and one of the rotor ironplates E is shown in FIG. 27. In FIG. 27, reference numeral 73represents magnet retaining holes, and when the rotor iron plates E arelaminated, the magnet retaining holes 73 are axially aligned with eachother as shown in FIG. 26 with the respective permanent magnets 74subsequently embedded therein.

[0164] Reference numeral 72 b 1 shown in FIG. 26 represents a rotor ironcore formed by laminating rotor iron plates F to an axial end face ofthe rotor iron core 72 a, one of the rotor iron plates F being shown inFIG. 28 in a plan view. In FIG. 28, reference numeral 77 representsmagnetic flux shortcircuit preventive holes that are arranged at thesame position as the magnet retaining holes 73 in the rotor iron platesE, but have a width U smaller than the width T of the magnet retainingholes 73. When the rotor iron plates F are laminated to the axial endface of the rotor iron core 72 a, the magnetic flux shortcircuitpreventive holes 77 are axially communicated with the magnet retainingholes 73 as shown in FIG. 26. In FIG. 26, reference numeral 72 c 1represents a rotor iron core made of one or more rotor iron plates Elaminated to the axial end face of the rotor iron core 72 b 1. Also, inFIG. 26, reference numeral 76 represents an end plate made of anon-magnetizable material and having a shape sufficient to overlay themagnet retaining holes 73 and the magnetic flux shortcircuit preventiveholes 77 so as to prevent debris of the permanent magnets 74, whichwould be generated at the time the permanent magnets 74 are inserted inand embedded in the magnet retaining holes 73, from flowing outwardlyand also to prevent external foreign matter from being trapped into themagnet retaining holes 73.

[0165] As shown in FIG. 26, an axial end face 79 of each of thepermanent magnets 79 is held in engagement with an outer peripheral edge78 of the respective magnetic flux shortcircuit preventive hole 77 on anabutment face of the rotor iron core 72 b 1 that is in engagement withthe rotor iron cores 72 a and, accordingly, magnetic fluxes 80 leakingbetween N and S poles at the respective opposite ends of the permanentmagnets 74 run from the rotor iron cores 72 a back to the permanentmagnets 74 through the rotor iron core 72 b 1, then across the magneticflux shortcircuit preventive holes 77- and finally through the rotoriron cores 72 b 1 and 72 a. The leaking magnetic fluxes 80 b 1 runs fromthe rotor iron cores 72 a back to the permanent magnets 74 through therotor iron core 72 b 1, then through the rotor iron core 72 c 1, acrossthe magnet retaining holes 73, again through the rotor iron core 72 c 1,the rotor iron core 72 b 1 and finally through the rotor iron core 72 a.Where the rotor iron core 72 b 1 is made up of a single rotor iron plateor a plurality of rotor iron plates F in a number as small as possibleso long as the permanent magnets can be positioned, a magnetic circuitthrough which the leaking magnetic fluxes 80 a 1 run can have a magneticresistance of a magnitude sufficient to minimize the leaking magneticfluxes 80 a 1. Also, since the width T of the magnet retaining holes 73in the rotor iron plate E forming the rotor iron core 72 c 1 is solarger than the width U of the magnetic flux shortcircuit preventivehole 77 in the rotor iron plate F that, as compared with the case inwhich the rotor iron core 72 c 1 is prepared from the rotor iron plateF, the magnetic circuit through which the leaking magnetic fluxes 80 b 1run can have a magnetic resistance of a magnitude sufficient to minimizethe leaking magnetic fluxes 80 b 1. Therefore, the motorcharacteristic-can be increased.

[0166] Also, since the permanent magnets 74 attracts and is thereforeheld in engagement with the outer peripheral edge 78 of the magneticflux shortcircuit preventive hole 77 in the rotor iron core 72 b 1, thepermanent magnets 74 can be accurately positioned with respect to theaxial direction thereof only by means of the rotor iron cores 72 with noholder employed, thereby reducing the cost for assembly and componentparts.

[0167] It is to be noted that the number of the rotor iron plates Flaminated is so chosen that a point intermediate of the axial length ofthe rotor iron cores 72 can match with a point intermediate of the axiallength of the permanent magnets 74, and this equally applies to any oneof the embodiments of the present invention that follow.

[0168] It is also to be noted that where the permanent magnets are madeof a rare earth metal of, for example, Nd—Fe—B system, since the magnetmade of the rare earth metal of the Nd—Fe—B system is known to exhibit ahigh residual magnetic flux density, the volume of the rotor and themotor as a whole can advantageously be reduced.

[0169] In describing the tenth embodiment of the present invention, thepermanent magnets has been employed in the form of a generallyplate-like configuration, but the present invention may not be limitedthereto and can be equally applied to the rotor employing the permanentmagnets of any suitable shape such as, for example, an arcuate shape.

[0170] Eleventh Embodiment (FIGS. 29 and 30)

[0171] An eleventh preferred embodiment of the present invention will bedescribed with reference to FIGS. 29 and 30, wherein FIG. 29 is alongitudinal sectional view of the rotor used in the synchronous motorand FIG. 30 is a plan view of the rotor iron plate G. As shown in FIG.29, reference numeral 72 d 1 represents a rotor iron core comprising arotor iron core 72 a having its axial end face to which rotor ironplates G are laminated. Since the rotor iron plates G have no magnetretaining hole defined therein, lamination of the rotor iron plates G tothe axial end face of the rotor iron core 72 a results closure of themagnet retaining holes 73.

[0172] Since the axial end face 81 of the permanent magnets 74 is heldin engagement with an abutment face of the rotor iron core 72 d 1 thatis held in engagement with the rotor iron core 72 a, magnetic fluxes 80c 1 leaking from the axial end of the permanent magnets 74 runs from therotor iron core 72 a back to the permanent magnets 74 through the rotoriron core 72 d 1 and then through the rotor iron core 72 a. Also, sincethe permanent magnets 74 attract and are therefore held in engagementwith the axial end face 82 of the rotor iron core 72 d 1, the permanentmagnets 74 can be accurately positioned with respect to the axialdirection thereof with no need to use any holder, thereby reducing thecost for assembly and component parts.

[0173] Also, since the magnet retaining holes 73 in the rotor iron core72 a are closed at one end by the rotor iron core 72 d 1, positioning ofa single end plate 76 at the opposite end is sufficient to close theopposite ends of the magnet retaining holes 73. While in the previouslydescribed tenth embodiment of the present invention, two end plates 76are required, the eleventh embodiment requires the only end plate 6 and,therefore, the cost for assembly and component parts can further bereduced.

[0174] The rotor iron plate E and the rotor iron plate G can easilymanufactured by controlling loading and unloading of blanking dies, thatare used to form the magnet retaining hole 73, during a blankingprocess. Therefore, no blanking dies that are required in the previouslydescribed tenth embodiment of the present invention to form the magneticflux shortcircuit preventive hole 77 in the rotor iron plate F isneeded, making it possible to simplify the structure of the diesthemselves.

[0175] Twelfth Embodiment (FIG. 31)

[0176]FIG. 31 illustrates a longitudinal sectional view of the rotorused in the synchronous motor according to a twelfth embodiment of thepresent invention. An axial end face of the rotor iron core 72 d 2opposite to that with which the axial end face 81 of the permanentmagnets 74 are held in engagement is provided with a rotor iron core 72c 2 of a laminated structure including rotor iron plates E.

[0177] Since the axial end face 81 of the permanent magnet 74 is held inengagement with the axial end face 82 of the rotor iron core 72 d 2,magnetic fluxes 80 c 2 leaking at the axial end of the permanent magnet74 run from the rotor iron core 72 a back to the permanent magnet 74through the rotor iron core 72 d 2 and then through the rotor iron core72 a. The leaking magnetic fluxes 80 b 2 runs from the rotor iron cores72 a back to the permanent magnet 74 through the rotor iron core 72 d 2,then through the rotor iron core 72 c 2, across the magnet retainingholes 73, again through the rotor iron core 72 c 2, the rotor iron core72 d 2 and finally through the rotor iron core 72 a.

[0178] Since the leaking magnetic fluxes 80 c 1 traverse the magnetretaining holes 73, as compared with the magnetic resistance of themagnetic circuit through which the leaking magnetic fluxes 80 c 1 run inthe previously described eleventh embodiment of the present invention,the magnetic circuit through which the leaking magnetic fluxes 80 b 2run in this twelfth embodiment has a relatively high magnetic resistanceand, therefore, the sum of the leaking magnetic fluxes 80 c 2 and 80 b 2in this twelfth embodiment is smaller relative to the leaking magneticfluxes 80 c 1 in the previously described eleventh embodiment.Accordingly, since the leaking magnetic fluxes can be reduced ascompared with that in the previously described embodiment, the motorcharacteristic can be increased.

[0179] Thirteenth Embodiment (FIGS. 32 to 34)

[0180] A thirteenth preferred embodiment of the present invention willbe described with reference to FIGS. 32 to 34. FIG. 32 illustrates alongitudinal sectional view of the rotor used in the synchronous motoraccording to the thirteenth embodiment of the present invention. In thisfigure, reference numeral 83 represents a rotor and reference numeral 84represents a rotor iron core. Reference numeral 84 a represents a rotoriron core made up of a laminate of rotor iron plates H. Referencenumeral 84 b represents a rotor iron core made up of a laminate of rotoriron plates 1, one of which is shown in FIG. 34 in a plan view.

[0181]FIG. 33 illustrates a plan view of the rotor iron plate H. In thisfigure, reference numeral 85 represents a plurality of slots foraccommodating conductor bars 86 a of the starter squirrel cageconductor, and reference numeral 73 represents magnet retaining holes.

[0182] Referring to FIG. 34, reference numeral 87 represents a pluralityof slots for accommodating the conductor bars 86 a of the startersquirrel cage conductor shown in FIG. 32, which slots 86 a are of thesame shape as the slots 85 in the rotor iron plate H and are positionedat the same position as the slots 85 in the rotor iron plate H.Reference numeral 77 represents magnetic flux shortcircuit preventiveholes that are positioned at the same position as the magnet retainingholes 73 in the rotor iron plate H of FIG. 33, but have a width Usmaller than the width T of the magnet retaining holes 73.

[0183] Referring back to FIG. 32, reference numeral 84 c represents arotor iron core made up of one rotor iron plate E or a laminate of rotoriron plates E. By the use of any known aluminum die casting technique,the conductor bars 86 a and shortcircuit rings 86 b are formedintegrally together to define the starter squirrel cage conductor. Byarranging the starter squirrel cage conductor in the rotor 83, theself-starting synchronous motor of the type employing the permanentmagnets can be obtained which operates as an inductor motor at the timeof starting thereof and as a synchronous motor entrained by asynchronous speed upon arrival at the synchronous speed. Even in thiscase, since as is the case with the previously described tenthembodiment of the present invention, the rotor iron core 84 b having themagnetic flux shortcircuit preventive holes 77 defined therein areemployed and the rotor iron plates E are laminated, the leaking magneticfluxes between the N and S poles at the axially opposite ends of thepermanent magnets 74 can be reduced, thereby increasing the motorcharacteristic.

[0184] Even in the self-starting synchronous motor of the type employingthe permanent magnets in which the starter squirrel cage conductor isarranged such as in this thirteenth embodiment, the permanent magnets 74can be accurately positioned only by the rotor iron core 84 with no needto employ any holder and, therefore, the cost for assembly and componentparts can be reduced advantageously.

[0185] Fourteenth Embodiment (FIGS. 35 to 37)

[0186] A fourteenth preferred embodiment of the present invention willbe described with reference to FIGS. 35 to 37, wherein FIG. 35illustrates a longitudinal sectional view of the rotor used in thesynchronous motor according to the fourteenth embodiment of the presentinvention, FIG. 36 illustrates a plan view of an electromagnetic steelplate J positioned inwardly of opposite axial ends of the rotor, ironcore and FIG. 37 illustrates a plan view of an electromagnetic steelplate K positioned at the opposite axial ends of the rotor iron core.

[0187] Referring now to FIGS. 35 to 37, reference numeral 91 representsa rotor, and reference numeral 92 represents a rotor iron core of alaminated structure including the electromagnetic steel plates J 110 andthe electromagnetic steel plates K 111. The electromagnetic steel platesJ 110 and K 111 are formed with respective conductor bar slots 112 ofthe same size, respective barrier slots 113 of the same size forpreventing the magnetic flux shortcircuit, respective holes 99 of thesame size and respective bearing holes 114 of the same size, which arealigned with each other. Reference numerals 96 b and 96 a representmagnet retaining holes defined at the same position, wherein respectivehole widths R and S as measured in a direction radially thereof are sochosen as to satisfy the relationship R<S.

[0188] Reference numeral 93 represents conductor bars made of aluminumand filled in the respective slots 112. The conductor bars 93 areintegrally molded together with the shortcircuit rings 94 at the axiallyopposite ends of the rotor iron core 92 by means of any known aluminumdie casting technique to thereby form the starter squirrel cageconductor. Reference numeral 95 represents permanent magnets, every twoof which are, after the aluminum die casting, held in end-to-endabutment to represent a generally V-shaped configuration and are theninserted and arranged in the magnet retaining holes 96 and 96 a so thatthe two pairs of the permanent magnets 95 can define two magnetic poles.The barrier slots 113 are filled; up with aluminum injected during thealuminum die casting to avoid any possible shortcircuit between theneighboring permanent magnets of the different polarities. Referencenumeral 98 represents a non-magnetizable end plate for protection of thepermanent magnets 95, which end plate has an engagement hole 98 adefined therein. Reference numeral 99 represents an axial hole definedin the rotor iron core 92 so as to extend axially thereof, in which holeis filled aluminum 100 that is injected during the aluminum die castingto form the starter squirrel cage conductor. The aluminum 100 filled inthe axial hole 99 has projections 100 a protruding outwardly from theaxially opposite ends of the rotor iron core 92. The end plates 98 are,after the engagement holes 98 a have received therein the projections100 a, fixed to the respective axial end faces of the rotor iron core 92by staking or crimping the projections 100 a to enlarge as shown bybroken lines. Reference numerals 101 and 114 represents respectivebearing holes.

[0189] It is to be noted that although in the foregoing description thepermanent magnets which have been magnetized are inserted and arranged,the rotor magnetic poles may be equally formed by inserting andarranging permanent magnets, which have not yet been magnetized, in therotor iron core to complete the rotor and then polarizing the permanentmagnets with the use of a magnetizing apparatus.

[0190] During the manufacture of the self-starting synchronous motor ofthe structure described above, and at the time the shortcircuit rings 94formed by the aluminum die casting cool, the outer diameter of themagnet retaining holes 96 a in the electromagnetic steel plates K 111 ateach axial end of the rotor iron core 92 deforms and contracts under theinfluence of a force of shrinkage acting in an inner radial direction.However, since the hole width S of the magnet retaining holes 96 a issufficiently larger than the hole width R of the magnet retaining hole96 in the electromagnetic steel plates J that are small of the shrinkageforce of the shortcircuit rings 94, there is no possibility that as aresult of reduction in gap between the permanent magnets 95 b and themagnet retaining holes 96 a that is brought about by deformation andshrinkage insertion of the permanent magnets 95 into the respectivemagnet retaining holes 96 a is difficult to achieve.

[0191] The hole width S of the magnet retaining holes 98 a is so chosenas to be slightly greater than R by a quantity that a side adjacent anouter diameter of the hole width S when receiving the shrinkage force ofthe shortcircuit ring 94 can line up with a side adjacent an outerdiameter of the hole width R of the magnet retaining hole 96, andaccordingly, a possibility can be avoided which would, as a result ofreduction of the coefficient of permeance of the magnetic circuit can belowered, the motor characteristic may correspondingly decrease.

[0192] As hereinabove described, the self-starting synchronous motor ofthe type employing the permanent magnets according to the fourteenthembodiment is advantageous in that the permanent magnets 5 can be easilyinserted subsequent to the aluminum die casting and that ahigh-performance motor characteristic can be maintained.

[0193] Fifteenth Embodiment (FIGS. 38 and 39)

[0194] A fifteenth preferred embodiment of the present invention will bedescribed with reference to FIGS. 38 and 39 in combination with FIGS. 36and 37. FIG. 38 is-a longitudinal sectional view of the rotor used inthe self-starting synchronous motor of the type employing the permanentmagnets according to the fifteenth preferred embodiment of the presentinvention, and FIG. 39 is a plan view of the electromagnetic steel plateL at one end face of the rotor iron core 92 of FIG. 38.

[0195] Referring now to FIGS. 38 and 39, one or a plurality ofelectromagnetic steel plates L 120 at one end of the rotor iron core onthe P side have no magnet retaining hole defined therein. Theelectromagnetic steel plates on the axially opposite ends of the rotoriron core 92 are laminated with the same electromagnetic steel plates K111 as those shown in FIG. 37 in connection with the fourteenthembodiment and the electromagnetic steel plates J 110 are laminatedinwardly of the opposite ends. Since the axial end face of the permanentmagnets abuts against the electromagnetic steel plate L, the number ofthe electromagnetic steel plates L laminated is so chosen thatrespective axial centers of the rotor iron core and the permanentmagnets can match with each other.

[0196] In the fifteenth embodiment of the present invention which is soconstructed as hereinabove described, since the rotor 91 is such thatone or a plurality of the electromagnetic steel plates L 120 at the endof the rotor iron core 92 on the P side has no magnet retaining holedefined therein, the only end plate 98 is sufficient on the opposite Qside and, therefore, the cost for material and the number of fittingsteps can be reduced advantageously. Also, since the hole width S of themagnet retaining holes 96 a in the electromagnetic steel plates K 111 onthe axially opposite ends of the rotor iron core 2 is sufficientlygreater than the hole width R of the magnet retaining holes 96 in theinside electromagnetic steel plates J 110, even though a radiallyinwardly shrinking deformation occurs under the influence of theradially inwardly acting shrinkage force from the shortcircuit rings 94subsequent to the aluminum die casting, the permanent magnets 95 can becarried out without being disturbed and, since as is the case with thefirst embodiment of the present invention, the gaps between thepermanent magnets 95 b and the magnet retaining holes in the rotor ironcore 92 are properly maintained, a high-performance motor characteristiccan be maintained.

[0197] Sixteenth Embodiment (FIG. 40)

[0198] A sixteenth preferred embodiment of the present invention will bedescribed with reference to FIG. 40 in combination with FIGS. 36 to 38.FIG. 40 is a longitudinal sectional view of the rotor employed in theself-starting permanent magnet synchronous motor according to thesixteenth embodiment. As shown in FIG. 40, one or a plurality ofelectromagnetic steel plates L 120 shown in FIG. 40 and having no magnetretaining holes defined therein are laminated to one end of the rotoriron core 92 on the P side, and one or a plurality of electromagneticsteel plates K 111 having the magnet retaining holes of a relativelygreat hole width are laminated to the opposite end of the rotor ironcore 92 on the Q side. Since no magnet retaining hole is defined in theelectromagnetic steel plates L 120 on the P side end, the shrinkagestress of the shortcircuit ring 94 has no concern therewith and,therefore, the permanent magnets 95 can easily be inserted in the rotoriron core 92 if the electromagnetic steel plates K 111 having the magnetretaining holes 96 of a relatively great hole width are arranged only onthe Q side. Accordingly, the rotor iron core 92 can be assembled with aminimized combination of the electromagnetic steel plates J 110, K 111and L 120, thereby facilitating the manufacture thereof and alsomaintaining a high-performance motor characteristic.

[0199] Seventeenth Embodiment (FIGS. 41 and 42)

[0200] A seventeenth preferred embodiment of the present invention willbe described with reference to FIGS. 41 and 42 in combination with FIG.39. FIG. 41 is a longitudinal sectional view of the rotor employed inthe self-starting permanent magnet synchronous motor according to theseventeenth embodiment and FIG. 42 is an end view of the synchronousmotor viewed from the P side in FIG. 41.

[0201] The basic structure of the rotor in the seventeenth embodiment issubstantially similar to that described in connection with any of thefifteenth and sixteenth embodiments.

[0202] Referring to FIGS. 41 and 42, the shortcircuit ring 94 a having areduced inner diameter is formed on an outer end face of theelectromagnetic steel plates L 120 shown in FIG. 39 and having no magnetretaining hole defined therein on the P side, by means of the aluminumdie casting. The inner diameter of the shortcircuit ring 94 a is suchthat it can be enclosed inwardly of the whole of the magnet retainingholes 96 and 96 a defined respectively in the electromagnetic steelplates j and K as shown by the broken lines, or partly inwardly thereofalthough not shown. Since the electromagnetic steel plates L 120 have nomagnet retaining hole such as identified by 96, there is no possibilitythat during the aluminum die casting aluminum may penetrate into themagnet retaining holes 96. In view of the foregoing, the shortcircuitring 94 a can have an increased cross-sectional surface area to therebyreduce a secondary resistance of the rotor, the rotational speed of themotor at the time of a maximum torque en route the synchronous speed andthe at the time of the maximum torque can increase to facilitate asynchronous entanglement, thereby increasing the starting performance ofthe motor.

[0203] Eighteenth Embodiment (FIG. 43)

[0204] An eighteenth preferred embodiment of the present invention willbe described with reference to FIG. 43 which shows a plan view of anelectromagnetic steel plate M for the rotor of the self-startingpermanent magnet synchronous motor according to the eighteenthembodiment.

[0205] The basic structure of the rotor in the eighteenth embodiment issubstantially similar to that described in connection with any of theeighteenth and seventeenth embodiments. Referring now to FIG. 43,reference numeral 131 represents entwining portions for lamination ofthe electromagnetic steel plates. As shown in FIG. 43, when theelectromagnetic steel plates are blanked one by one, press projectionsare formed and are laminated together while sequentially entwinedtherewith to thereby form the rotor iron core. In such case, theentwining portions 131 are defined at respective locations outwardly ofthe magnet retaining holes 132. Reference numeral 132 a represents anenlarged portion in which the hole width of a portion of each magnetretaining hole 132 adjacent the corresponding entwining portion 131 isenlarged radially outwardly by a required quantity V towards suchcorresponding entwining portion 131. Reference numeral 133 represents apincer portion of the electromagnetic steel plate M 130 bound betweenthe corresponding entwining portion 131 and the enlarged portion 132 aof each magnet retaining hole.

[0206] According to the eighteenth embodiment, since the provision hasbeen made of the enlarged portion 132 a in which the hole width of eachmagnet retaining hole adjacent the corresponding entwining portion 131is increased by the quantity V towards the entwining portion 131, eventhough the corresponding pincer portion 133 is deformed to protrudeinwardly of the associated magnet retaining hole 132 under the influenceof press stresses during formation of the corresponding entwiningportion by the use of a press work, the deformation can be accommodatedwithin the enlarged quantity V and, therefore, the permanent magnet caneasily be inserted without being disturbed. Also, since the enlargedportion 132 a has a length W that is small in correspondence with thelength of the adjacent entwining portion 131 and, also, the specificvalue of the quantity V is small and will decrease in response to inwarddeformation of the pincer portion 133, the gap with the permanent magnetis very minute and the coefficient of permeance of the magnetic circuitwill not decrease substantially, thereby securing a high-performancemotor characteristic.

[0207] It is to be noted that in the foregoing description the entwiningportion 131 has been described as positioned outside the associatedmagnet retaining hole 132, but it may be positioned inside theassociated magnet retaining hole and even in this case similar effectscan be obtained.

[0208] It is also to be noted that since if each of the permanentmagnets is made of a rare earth metal of, for example, Nd—Fe—B system, ahigh magnetic force can be obtained and, therefore, the rotor and themotor as a whole can advantageously be manufactured in a compact sizeand lightweight.

[0209] It is further to be noted that although in the foregoingembodiment reference is made to the rotor of the synchronous motoremploying the two poles, the present invention may not be limitedthereto and may be equally applied to the rotor having, for example,four or more magnetic poles.

[0210] Again, although in any one of the foregoing embodiments thesingle pole has been formed by abutting two plate-like permanent magnetsof the same polarity in end-to-end fashion, the present invention maynot be limited thereto and the single pole may be formed by the use of asingle permanent magnet or three or more plate-like permanent magnets ofthe same polarity. Similarly, although the permanent magnets have beenemployed in the plate-like form, the present invention is not limitedthereto and the present invention is equally applicable to the rotoremploying permanent magnets of, for example, an arcuate shape or anyother suitable shape.

[0211] Nineteenth Embodiment (FIGS. 45 to 47)

[0212] A nineteenth preferred embodiment of the present invention willnow be described with reference to FIGS. 45 to 47, wherein FIG. 45illustrates a longitudinal sectional view of the rotor used in theself-starting synchronous motor of the type employing the permanentmagnets according to the nineteenth embodiment, FIG. 46 is a transversesectional view of the rotor and FIG. 47 is a plan view of an end plate.In these figures, reference numeral 141 represents a rotor, andreference numeral 142 represents a rotor iron core made of a laminate ofelectromagnetic steel plates. Reference numeral 143 represents conductorbars which are molded integrally together with shortcircuit rings 144,positioned at axially opposite ends of the rotor iron core 142, by theuse of the aluminum die casting technique to form a starter squirrelcage conductor. Reference numeral 145 represents permanent magnets,every two of which are held in end-to-end abutment to represent agenerally V-shaped configuration and are so arranged that the two pairsof the permanent magnets 145 can define two magnetic poles. Referencenumeral 147 represents shortcircuit preventive barriers for preventingshortcircuit of the magnetic fluxes between the permanent magnets of thedifferent polarities and filled up with aluminum die cast. Referencenumeral 148 represents an end plate made of a non-magnetizable materialand used of protection of the permanent magnets 145, in which engagementholes 148 a are defined. Reference numeral 149 represents an axial holedefined in the rotor iron core 142 so as to extend axially thereof, inwhich hole is filled aluminum 150 that is injected during the aluminumdie casting to form the starter squirrel cage conductor. The aluminum150 filled in the axial hole 149 has projections 150 a protrudingoutwardly from the axially opposite ends of the rotor iron core 142. Theend plates 148 are, after the engagement holes 148 a have receivedtherein the projections 150 a, fixed to the respective axial end facesof the rotor iron core 142 by staking or crimping the projections 150 ato enlarge as shown by broken lines.

[0213] As hereinabove described, in the self-starting synchronous motoraccording to the nineteenth embodiment, since the projections 150 a usedto secure the end plates 148 to the axially opposite ends of the rotor141 are formed simultaneously with formation of the starter squirrelcage conductor by the use of the aluminum die casting technique andsince the end plates 148 can be firmly secured to the axially oppositeend faces of the rotor iron core 142 merely by staking or crimping theprojections 150 a, the cost for the material and the number ofassembling steps can be considerably reduced as compared with the priorart in which bolts are employed, thereby making it possible to providean inexpensive self-stating synchronous motor of the kind employing thepermanent magnets.

[0214] Twentieth Embodiment (FIGS. 48 to 50)

[0215] A twentieth preferred embodiment of the present invention willnow be described with reference to FIGS. 48 to 50, wherein FIG. 48 is alongitudinal sectional view of the self-starting permanent magnetsynchronous motor, FIG. 49 is a plan view of the end plate used in thesynchronous motor shown in FIG. 48, and FIG. 50 is a cross-sectionalview taken along the line C-C′ in FIG. 49. As shown in FIG. 48, theshortcircuit rings 144 a are formed so as to cover the end plates 152.Accordingly, the end plate 152 is integrated with the axially end faceof the rotor iron core 152 by means of the aluminum die casting used toform the starter squirrel cage conductor.

[0216] Referring to FIGS. 49 and 50, the end plate 152 is formed withtwo projections 152 a each having a respective hole 152 defined thereinso as to extend completely across the thickness thereof. Prior to thealuminum die casting, the end plate 152 is secured to the correspondingend face of the rotor iron core 142 with the projections 152 aprotruding through the holes 149 to thereby position the respective endplate 152 so that the end plate 152 will not displace during thealuminum die casting in which a high pressure may act on the end plate152 to allow the end plate 152 to be firmly connected to the associatedend face of the rotor iron core 142 without being displaced in position.On the other hand, the end plate 148, the end plate 148 is, as is thecase with that in the previously described nineteenth embodiment, fixedto the end face of the rotor iron core 142 by staking or crimping theprojections 150 a after the end plate 148 has been engaged with theprojections 150 a for fixing the end plate.

[0217] As hereinabove described, since the end plate 152 is integrallyconnected with the rotor iron core 142 by means of the aluminum diecasting, a job of securing the end plate by staking or crimping theprojections 150 a has to be performed only in association with the endplate 148 and, therefore, as compared with the previously describednineteenth embodiment, the number of assembling steps can further bereduced.

[0218] Twenty-first Embodiment (FIGS. 51 and 52)

[0219] A twenty-first preferred embodiment of the present invention willbe described with reference to FIGS. 51 and 52, wherein FIG. 51illustrates a longitudinal sectional view of the rotor used in theself-starting synchronous motor and FIG. 52 is a plan view of anelectromagnetic steel plate positioned at an axial end of the rotor ironcore used in the rotor of FIG. 51. Referring to FIGS. 51 and 52, theelectromagnetic steel plate 160 positioned at the axial end of the rotoriron core 142 having conductor bar slots 161, barrier holes 162 forpreventing the magnetic flux shortcircuit, holes 149 and a bearing hole150 all defined therein is of the same shape as that used at a differentposition, but no magnet retaining hole 146 defined therein. Althoughthis electromagnetic steel plate 160 is manufactured by blanking withthe use of the same core dies as used for the other electromagneticsteel plates, since mold pieces used to form the magnet retaining holes146 in the electromagnetic steel plate 160 by the use of a blankingtechnique are of a type that can be removably mounted on a die assembly,it is easy to avoid formation of the magnet retaining holes 146 in theelectromagnetic steel plate 160 at the time the latter is blanked offfrom a metal sheet. Accordingly, the rotor iron core 142 can beintegrally formed together with the electromagnetic steel plate 160 and,if this is aluminum die cast, the starter squirrel cage conductor can beformed.

[0220] Because of the structure described-above, the end plate on theother end is needed and, as is the case with the previously describedtwentieth embodiment, a job of securing the end plate by staking orcrimping the projections 150 a has to be performed only in associationwith the end plate 148 and, therefore, as compared with the previouslydescribed nineteenth embodiment, the number of assembling steps canfurther be reduced.

[0221] Twenty-second Embodiment (FIGS. 53 and 54)

[0222] A twenty-second preferred embodiment of the present inventionwill now be described with reference to FIGS. 53 and 54, wherein FIG. 53is a plan view of the electromagnetic steel plate at the axial end ofthe rotor iron core and FIG. 54 is a fragmentary enlarged view showing aportion of the rotor 141.

[0223] Referring to FIGS. 153 and 154, reference numeral 162 representsan electromagnetic steel plate disposed at an axial end of the rotoriron core 141, and reference numeral 164 represents a projectionprotruding inwardly of the permanent magnets 154 at a location where theelectromagnetic steel plate 163 engages the permanent magnets 145.Accordingly, the permanent magnets 145 are axially positioned with theprojection 164 in the electromagnetic steel plate 163 brought intoengagement therewith.

[0224] According to the embodiment shown in FIGS. 53 and 54,shortcircuit of the magnetic fluxes between the front and rear,different poles of the permanent magnets 145 through the electromagneticsteel plate 163 can be reduced considerably, thereby to increase theperformance of the motor. It is to be noted that although thiselectromagnetic steel plate 163 is manufactured by blanking with the useof the same core dies as used for the other electromagnetic steelplates, since mold pieces used to form the projection 163 are of a typethat can be removably mounted on a die assembly, the rotor iron core 142can easily be formed integrally together with the electromagnetic steelplate 163.

[0225] Twenty-third Embodiment (FIGS. 55 to 57)

[0226] A twenty-third embodiment of the present invention will bedescribed with reference to FIGS. 55 to 57, wherein FIG. 55 is alongitudinal sectional view of the complete rotor used in theself-starting synchronous motor according to this embodiment, FIG. 56 isa longitudinal sectional view of the rotor before the end plates arefixed, and FIG. 57 is an end view of the rotor shown in FIG. 56.Referring to FIGS. 56 and 57, the end plate 171 has its outer peripheryformed with radial projections 171 a and, on the other hand, theshortcircuit ring 170 formed by the aluminum die casting has an innerperiphery formed with a radial recesses 170 a complemental in shape tothe radial projections 171 a in the end plate 171. After the radialprojections 171 a in the end plate 171 have been engaged in thecorresponding radial recesses 170 a in the shortcircuit ring 170,peripheral portions of the radial recesses 170 a in the shortcircuitring 170 are axially pressed to deform as shown by 170 b in FIG. 55 tothereby fix the end plate 171 to the rotor iron core 2.

[0227] According to the twenty-third embodiment, fixing of the end plate171 can easily be accomplished merely by pressing the radial recesses170 a in the shortcircuit ring 170 to deform in the manner describedabove and, therefore, the number of assembling steps can advantageouslybe reduced.

[0228] It is to be noted that where the permanent magnets is made of arare earth metal of, for example, Nd—Fe—B system, a strong magneticforce can be obtained and, therefore, the rotor as well as the motor asa whole can be manufactured in a compact size and lightweight.

[0229] It is also to be noted that in any one of the foregoingembodiments the rotor has been shown having two magnetic poles, it mayhave four or more magnetic poles. In addition, although in any one ofthe foregoing embodiments the single pole has been formed by abuttingtwo plate-like permanent magnets of the same polarity in end-to-endfashion, the present invention may not be limited thereto and the singlepole may be formed by the use of a single permanent magnet or three ormore plate-like permanent magnets of the same polarity. Similarly,although the permanent magnets have been employed in the plate-likeform, the present invention is not limited thereto and the presentinvention is equally applicable to the rotor employing permanent magnetsof, for example, an arcuate shape or any other suitable shape.

[0230] Twenty-fourth Embodiment (FIGS. 60 to 62)

[0231] A twenty-fourth preferred embodiment of the present inventionwill now be described with reference to FIGS. 60 to 62, wherein FIG. 60illustrates a longitudinal sectional view of the rotor used in theself-starting synchronous motor according to this embodiment, FIG. 61 isa transverse sectional view of the rotor shown in FIG. 60 and FIG. 62 isa fragmentary enlarged view showing an encircled portion indicated by196 in FIG. 61.

[0232] Referring now to FIGS. 60 to 62, reference numeral 181 representsa rotor, and reference numeral 182 represents a rotor iron core made ofa laminate of electromagnetic steel plates. Reference numeral 183represents conductor bars that are formed integrally together withshortcircuit rings 184, positioned at axially opposite ends of the rotoriron core 182, by the use of an aluminum die casting technique to form astarter squirrel cage conductor. Reference numeral 185 representspermanent magnets accommodated within magnet retaining holes 186, witheach pair of plate-like permanent magnets 185 of the same polaritybutted end-to-end in a generally V-shaped configuration to form a singlerotor magnetic pole. Since four permanent magnets 185 are employed inthe rotor, two rotor magnetic poles are formed and, thus, the rotor as awhole has two magnetic poles.

[0233] A bridge portion indicated by 187 is so shaped as to have itswidth including a narrow portion 187 a and a large-width portion 187 bincreasing in width in a direction radially outwardly from the narrowportion 187 a. Shortcircuit of the magnetic fluxes between front andrear, opposite poles of the permanent magnets 185 can advantageously beprevented since magnetic saturation takes place at the narrow portion187 a.

[0234] Also, since an air space 188 is defined between each ofrespective end faces 185 a of the neighboring permanent magnets 185 andthe bridge portion 187, shortcircuit of the magnetic fluxes between theopposite poles within the end faces 185 a of the neighboring permanentmagnets 185 can advantageously be avoided.

[0235] Reference numeral 189 represents barrier slots for prevention ofthe magnetic flux shortcircuit that are defined between the neighboringpermanent magnets 185 of the different polarities, which slots arefilled up with aluminum injected during the aluminum die casting. Abridge portion 191 of the rotor iron core 182 between each barrier-slot189 and each magnet retaining hole 186 is so shaped as to have a smallwidth, and at this bridge portion 191, magnetic saturation takes placeto prevent the magnetic fluxes emanating from the opposite poles of thepermanent magnets 185 from shortcircuiting. Also, an air space 192 isformed between an end face of each permanent magnet 185 and the adjacentbridge portion 191 to prevent the magnetic fluxes from the oppositepoles within the end faces of the permanent magnets 185 fromshortcircuiting. Reference numeral 193 represents an end plate made of anon-magnetizable material for protecting the permanent magnets 185. Thisend plate 193 is riveted to axially opposite end faces of the rotor ironcore 182 by means of rivet pins 194. Reference numeral 195 represents abearing hole defined in the rotor.

[0236] According to the twenty-fourth embodiment, the rotor 181 can beassembled by embedding the permanent magnets 185 in the respectivemagnet retaining holes 186 after the starter squirrel cage conductor hasbeen formed by the aluminum die casting in the rotor iron core 182 madeof a laminate of the electromagnetic steel plates, and subsequentlyriveting the end-plate 193 to each of the axially opposite end faces ofthe rotor iron core 182 by means of the rivet pins 194.

[0237] While after the aluminum die casting the shortcircuit rings willshrink in a radial direction during cooling of the aluminum, the rotoriron core 182 is also affected by a radially inwardly acting shrinkagestress. However, since the bridge portion 191 of the rotor iron core 182is provided on each sides of each of the barrier slots 189 at a locationadjacent the respective barrier slot 198 as shown in FIG. 58, a strengthagainst the shrinkage stress is so high that circumferential shrinkagestrains of an outer diameter of the rotor iron core 182 can be small.

[0238] On the other hand, since the bridge portion 187 is provided onlyat one location, strain acting in an inner diametric direction of therotor iron core 182 at this portion is large. In order to avoid this,the length in a radial direction of the narrow portion 187 a of thebridge portion 187 for prevention of the magnetic flux shortcircuit bymagnetic saturation is reduced and, on the other hand, the large-widthportion 187 b is provided next to the narrow portion 187 a, whereforethe strength against the radial shrinkage stress of the bridge portion187 as a whole is made strong to prevent the strain from occurring in aninner diametric direction of the rotor iron core 182 at a locationadjacent the bridge portion 187.

[0239] As such, the rotor iron core 182 can have an outer diameter of ashape substantially similar to the right round shape and, therefore, ifthe outer diameter thereof is so chosen at the time of blanking theelectromagnetic steel plates of the rotor iron core 182 that gap betweenthe outer diameter thereof and an inner diameter of the rotor iron corecan be of a predetermined dimension, a step of grinding or milling theouter diameter of the rotor iron core after the aluminum die casting toprovide the gap of the predetermined dimension can be dispensed with.

[0240] Although in any one of the foregoing embodiments the single polehas been formed by abutting two plate-like permanent magnets of the samepolarity in end-to-end fashion, the present invention may not be limitedthereto and the single pole may be formed by the use of a singlepermanent magnet or three or more plate-like permanent magnets of thesame polarity. Similarly, although the permanent magnets have beenemployed in the plate-like form, the present invention is not limitedthereto and the present invention is equally applicable to the rotoremploying permanent magnets of, for example, an arcuate shape or anyother suitable shape.

[0241] Thus, according to the twenty-fourth embodiment of the presentinvention, not only can any possible shortcircuit of the magnetic fluxesbetween the permanent magnet be prevented to secure a high performance,but also the grinding of the outer diameter of the rotor is eliminated,thereby making it possible to provide the high-performance, inexpensiveself-starting synchronous motor.

[0242] Twenty-fifth Embodiment (FIG. 63)

[0243]FIG. 63 illustrates a plan view of an electromagnetic steel plateused to form the rotor in the self-starting synchronous motor accordingto this embodiment. Referring now to this figure, reference numeral 51represents an electromagnetic steel plate, a plurality of which arelaminated together to form the rotor iron core. After the rotor ironcore has been so formed, the rotor iron core is subjected to thealuminum die casting to form the starter squirrel cage conductor in therotor iron core. Reference numeral 203 represents magnet retainingholes; reference numeral 204 represents a bridge portion F for each pairof the permanent magnets; reference numeral 205 represents barrier slotsfor prevention of shortcircuit of the magnetic fluxes; reference numeral206 represents a bridge portion; reference numeral 207 represents rivetholes through which rivets are passed to secure the end plate to eachaxial end face of the rotor core; and reference numeral 208 represents abearing hole. The permanent magnets to be inserted after the aluminumdie casting are shown by double-dotted lines and the rotor has two rotormagnetic poles formed therein.

[0244] The electromagnetic steel plate 201 has an outer diameter that isset to an outer diameter R1 sufficient to allow a gap between the rotorand the inner diameter of the stator iron core at one end of the rotorto satisfy a predetermined dimension, which outer diameter R1progressively increases towards a center point of the rotor magneticpole so that the outer diameter R2 of the center portion of the rotormagnetic poles can be greater than the outer diameter R1. By blankingthe electromagnetic steel plate of the above described shape andlaminating a predetermined number of the electromagnetic steel plates toform the rotor iron core and after the starter squirrel cage conductorhas been formed by the use of the aluminum die casting, the permanentmagnets are mounted in the rotor iron core.

[0245] After the aluminum die casting, the shortcircuit rings (notshown) formed on the axially opposite end faces of the rotor iron coreof the starter squirrel cage conductor undergo a shrinkage in a radialdirection as they are cooled, accompanied by a radial shrinkage of theouter diameter of the rotor iron core under the influence of a shrinkageforce of the shortcircuit rings.

[0246] At this time, since the rotor magnetic pole ends of theelectromagnetic steel plates 201 of the rotor iron core have the bridgeportion 206 defined at two locations, the strength is so high againstthe shrinkage stress in the inner diametric direction that the outerdiameter R1 of the rotor iron core will not vary virtually. However,since at the center portion of the rotor magnetic poles the bridgeportion 264 is defined only at one location, the strength is so low thatthe outer diameter R2 of the rotor iron core will shrink in a radialdirection under the influence of the shrinkage stress. At this time, ifthe dimension of the outer diameter R2 is chosen to be R1 aftershrinkage, the outer diameter of the rotor iron core as a whole can bemaintained at a substantially round shape.

[0247] It is to be noted that although in FIG. 63 the circle of theouter diameter R1 after the shrinkage is shown by the double-dottedline, the difference in dimension between R1 and R2 are shownexaggerated to facilitate a better understanding.

[0248] Although in the foregoing embodiments the single pole has beenformed by abutting two plate-like permanent magnets of the same polarityin end-to-end fashion, the present invention may not be limited theretoand the single pole may be formed by the use of a single permanentmagnet or three or more plate-like permanent magnets of the samepolarity.

[0249] According to the twenty-fifth embodiment of the presentinvention, since the outer diameter of the rotor iron core after thealuminum die casting attains a shape substantially similar to the rightround shape, and since the gap between it and the inner diameter of thestator iron core can be formed by pre-blanking with the use of dies,there is no need to grind or mill the outer diameter of the rotor ironcore and, therefore, the number of assembling steps can be reduced.Also, since the aluminum die casting is carried out while the permanentmagnets and the end plates have not yet been fitted, the job can beeasily performed with no defect parts occurring and, in view of thosecumulative effect, the productivity can be increased.

[0250] Although the present invention has been described in connectionwith the preferred embodiments thereof with reference to theaccompanying drawings, it is to be noted that various changes andmodifications are apparent to those skilled in the art. Such changes andmodifications are to be understood as included within the scope of thepresent invention as defined by the appended claims, unless they departtherefrom.

What is claimed:
 1. A synchronous motor comprising: a stator including astator iron core having two-pole windings wound therearound, said statoriron core having an inner cylindrical surface; a rotor including a rotoriron core rotatably accommodated facing the inner cylindrical surface ofthe stator iron core, said rotor including a plurality of conductorbars, positioned adjacent an outer periphery of the rotor iron core, andshortcircuit rings, positioned at axially opposite ends of the rotoriron core, said conductor bars and shortcircuit rings being moldedtogether by aluminum die casting to form a starter cage conductor, saidrotor having a plurality of magnet retaining slots defined therein on aninner side of the conductor bars; and permanent magnets embedded withinthe magnet retaining holes in the rotor and defining two magnetic polesof different polarities; said shortcircuit rings having an innerdiameter positioned outwardly from associated magnet retaining holes, aninner diameter of the shortcircuit rings at a location adjacent one endof the magnetic poles being larger than an inner diameter at a locationadjacent an intermediate point of the magnetic poles.
 2. The synchronousmotor as recited in claim 1, wherein the inner diameter of theshortcircuit rings on a side adjacent the permanent magnets lies outsidethe magnet retaining holes in the rotor iron core; wherein an innerdiameter of one of the shortcircuit rings adjacent one of the magneticwherein an inner diameter of one of the shortcircuit rings adjacent oneof the magnetic poles is larger than an inner diameter adjacent a pointintermediate the magnetic poles; and wherein an inner diameter of atleast one other of the shortcircuit rings lies inwardly of at least partof the magnet retaining holes; said synchronous motor further comprisingan end plate comprising a non-magnetizable material positioned betweenthe at least one other shortcircuit ring and the rotor iron core,covering the magnet retaining holes.
 3. The synchronous motor as recitedin claim 1, wherein the inner diameter of the shortcircuit rings on oneside of the permanent magnets lies outside the magnet retaining holes inthe rotor iron core; wherein an inner diametric dimension of one of theshortcircuit rings adjacent one end of the magnetic poles is greaterthan an inner diametric dimension of the one of the shortcircuit ringsadjacent the intermediate point of the magnetic poles; and wherein theinner diametric dimension of the at least one other of the shortcircuitrings lies inwardly of at least a part of the magnet retaining holes;said rotor iron core comprising a plurality of electromagnetic steelplates, one of the electromagnetic steel plates being adjacent the atleast one other shortcircuit ring, not formed with the magnet retainingholes.
 4. The synchronous motor as recited in claim 1, wherein the innerdiameter of the shortcircuit rings on one side of the permanent magnetscomprises a shape lying along the magnet retaining holes in the rotoriron core.
 5. A synchronous motor which comprises: a stator including astator iron core having a winding wound therearound, said stator ironcore having an inner cylindrical surface; a rotor including a rotor ironcore that is rotatably connected to the inner cylindrical surface of thestator iron core, said rotor including a plurality of conductor barsaccommodated within corresponding slots defined in an outer peripheralportion of the rotor iron core, said conductor bars having correspondingopposite ends shortcircuited by shortcircuit rings to form a startercage conductor, said rotor having a plurality of magnet retaining holespositioned on an inner side of the conductor bars; and a plurality ofpermanent magnets embedded within the plurality of magnet retainingholes in the rotor, the plurality of magnets defining a north rotormagnetic pole and a south rotor magnetic pole, each of the rotormagnetic poles having a center point and opposing end points; whereinthe slots in the outer peripheral portion of the rotor iron core areseparated by slot intervals, slot intervals adjacent to the opposing endpoints of each of the rotor magnetic poles being smaller than a slotinterval adjacent to the center point of each of the rotor magneticpoles.
 6. The synchronous motor as claimed in claim 5, wherein a slotinterval circumferentially adjacent to the slot interval adjacent to thecenter point of at least one of the rotor magnetic poles in a directionof rotation of the rotor is greater than a slot intervalcircumferentially adjacent to the slot interval adjacent to the centerpoint of the rotor magnetic pole in a direction opposite to thedirection of rotation of the rotor.
 7. The synchronous motor as claimedin claim 5, wherein the slots positioned adjacent to the center pointsof the rotor magnetic poles having shorter radial lengths than the slotspositioned adjacent to the end points of the rotor magnetic poles. 8.The synchronous motor as claimed in claim 5, wherein an inner end ofeach slot is positioned a predetermined distance from the rotor magneticpoles, the slots positioned adjacent to the end points of the rotormagnetic poles having shorter distances to the rotor magnetic poles thanthe slots not positioned adjacent to the end points of the rotormagnetic poles.
 9. The synchronous motor as claimed in claim 8, whereinthe distances between the slots and the rotor magnetic polesprogressively increase from the slots positioned adjacent to the endpoints of the rotor magnetic poles to the slots positioned adjacent tothe respective center points of the rotor magnetic poles.
 10. Asynchronous motor which comprises: a stator including a stator iron corehaving a winding wound therearound, said stator iron core having aninner cylindrical surface; a rotor including a rotor iron core that isrotatably connected to the inner cylindrical surface of the stator ironcore, said rotor including a plurality of conductor bars accommodatedwithin corresponding slots defined in an outer peripheral portion of therotor iron core, said conductor bars having corresponding opposite endsshortcircuited by respective shortcircuit rings to form a starter cageconductor, said rotor having a plurality of magnet retaining holespositioned on an inner side of the conductor bars; and a plurality ofpermanent magnets embedded within the plurality of magnet retainingholes in the rotor, the plurality of permanent magnets defining a northrotor magnetic pole and a south rotor magnetic pole, each of the rotormagnetic poles having a center point and opposing end points; whereineach of the slots has a corresponding radial length, a radial length ofa slot adjacent to the center point of each of the rotor magnetic polesbeing smaller than radial lengths of slots not adjacent to the centerpoint of each of the rotor magnetic poles; and wherein a distancebetween a slot, positioned adjacent one end of each of the rotormagnetic poles, and the magnet retaining holes corresponding to therotor magnetic poles is smaller than distances between slots, notpositioned adjacent to one end of each the magnetic poles, and thecorresponding magnet retaining holes.
 11. The asynchronous motor asclaimed in claim 10, wherein distances between the slots and the magnetretaining holes progressively increase from the position adjacent oneend of each of the rotor magnetic poles towards the position adjacentthe respective center point of each of the rotor magnetic poles.